Knowledge is invaluable. Furthering our understanding of how the universe came into being, and ultimately how we came into being, cannot be measured as useful solely in terms of cost. What price to pay for knowing that in the future, humanity can be saved because there are other planets out there capable of sustaining life?
Scientific knowledge has intrinsic worth. Space exploration is just one aspect of science that seems to have little impact on our daily lives. Who cares if the Higgs-Boson exists? Very few people. But governments have funded a new particle collider at CERN to find it because they recognise the importance of finding it to understanding the universe.

It's sickening to see all of these people going on and on about "saving the starving and impoverished". Well then sell your computer. Stop commenting on here, go dedicate your life to helping the "starving and needy". And how many tons of rice and grain do we need to keep dropping on these countries before they get their act together and FEED THEMSELVES. I know it sounds heartless, but it's their fault. I don't care if they don't have money. Man lived for thousands of years off of the land and many (dumb) animals still manage to pull it off. Why do we have to send some christian missionaries over to dig them a well? Why can't they dig their own well? Why can't they plant their own grain? Why can't they hunt their own game or raise their own livestock? Why can't they move OUT of the areas of drought? Why is it OUR problem? You feel guilty because you live better? We shouldn't help people that will not help themselves. And something is going to happen and we will ALL be dead or starving on this planet because we refused to move on and advance the survival of our species; all pissed away on supporting some people that would probably just as soon let us starve if we were the ones without food and they were the rich ones.

Compared to other areas of government spending (e.g. military), the cost of space exploration simply isn't ridiculously high. There have been space vehicles built in the private sector for as little as $25m, a drop in the ocean compared to US spending in Iraq, and the net benefits outweigh even these figures.

Without the urge to ‘see what’s out there’ the continents would still be populated by the indigenous races. North Americans would all be Native Americans, Africans would all be black, and Australia would have only Aborigines and kangaroos. Let’s take this argument to its extremities: Suppose no one had ever wondered if there was another little village somewhere in the world. Then every group of civilised people would have to grow in their own shell of ignorance. The printing press would have remained in Germany unless some other nation happened to stumble on the same process. The same would apply to…well, the list is just too long and life is too short.

Many discoveries and products have been developed from the knowledge gained from space exploration. For example, NASA created Velcro which is now used in many clothing items, bags and so forth. Non-stick pans and surfaces were also created as a result of space exploration. Now we can cook without worrying whether or not our cakes will stick to the sides of our pans. Overall, space exploration has provided us with new knowledge and as a result of this, many new and intriguing inventions have been made.

It's sickening to see all of these people going on and on about "saving the starving and impoverished". Well then sell your computer. Stop commenting on here, go dedicate your life to helping the "starving and needy". And how many tons of rice and grain do we need to keep dropping on these countries before they get their act together and FEED THEMSELVES. I know it sounds heartless, but it's their fault. I don't care if they don't have money. Man lived for thousands of years off of the land and many (dumb) animals still manage to pull it off. Why do we have to send some christian missionaries over to dig them a well? Why can't they dig their own well? Why can't they plant their own grain? Why can't they hunt their own game or raise their own livestock? Why can't they move OUT of the areas of drought? Why is it OUR problem? You feel guilty because you live better? We shouldn't help people that will not help themselves. And something is going to happen and we will ALL be dead or starving on this planet because we refused to move on and advance the survival of our species; all pissed away on supporting some people that would probably just as soon let us starve if we were the ones without food and they were the rich ones.

No one has ever said that space was not meant for us to cross, who is to say that the oceans were meant for us to cross into America? How many men died crossing the ocean to the Americas and other contintents? Much more then seven I can bet you, but I am not saying their death was pointless and for waste. They knew the risks, and they took it for the sake of knowledge.
It is also not meaningless, how is it meaningless? Many many many technologies have come out of it. (See The Largest Benefits)
Beyond the side effects, which were revolutionary in and of themselves, we may need Space more than we think. We all know, unless we're dillusional, that our planet won't last forever (found out through Space exploration, BTW), and that how long it lasts relies heavily on our surrounding environment. The more we know about out own Galaxy, and even just the Universe, the safer we can potentially make out planet. Besides, if we're not carefull, we're going to be emigrating to one of those planets out there sooner than we think. Where would we be if Earth became uninhabitable and we, having cut our Space program, were unable to find a substitute?

Space travel has given us a lot of new things for example the micro chip, the CAT scan and so on. You might say that we could just put together a group of scientist to figure it out, but and idea has to come from something, and they wouldn't just make a CAT scan if someone told to to make something to scan a brain, and even if they would, it would take a lot more time. Also, space travel could benefit our future, if we ended up making settlements on the moon or mars, we might be able to mine there and get rare minerals, or a huge supply of a mineral, boosting economy. Think of America, if someone had put a stop to earth's exploration due to poverty, we wouldn't have one economically strong country(USA) to help the poor.

Plastic were invented by material engineers working on the space program. it is a large, profitable, and useful industry. Parts of your computer are made of it. Innovations in computing were needed. More efficient fuels were researched. The Internet was a joint military and NASA project. Obviously you are taking advantage of them right now.

Why do people wan't more money, just to have smex with different women (Like at the South park episode Sexual Healing) or they just to stay at Earth not knowing that one day Earth maight be reduced to a Mars-Like planet. There are extraterrestrials or Extrajovians (not Jupiter or any thing else outside the habitable zone) that seem friendly (Hollywood makes them evil just so humans can feel good about themselves). A Solar System is not a Galaxy as many people who believe in sky spirits still discredit today. There is always a way to travel there not just by using simple rockets or shuttles or anything that the people that don't know what the new things that the scientists thought about. There will come a time when an organism is taken from Gliese, COROT or PSR to Earth and shown to those guys who still believes in magic making and they'll say "Oo thats fake thats just a cat in FrogChickenleg costume and aliens don't exist blah blah blah" like some thing that you pray to actually help you? I tried once and all I get is embarressment and mockery and everything bad that happens...(whoever reads this and notices that i'm off the subject please don't comment "dude you suck all I read was blah blah i hate religion blah blah aliens exist...) please hesitate to type...

Space Exploration has given us many,many technologies that are essential.

Satellites were some of the first venturers into space and are another critical part of our society.

Weather Forecasting (Satellites. Very important for hurricanes and dangerous storm systems, have saved lives and help us prepare for the worst.)

Velcor and non-stick pans! (Mostly a joke, but hey, they work!) (General Technology.)

GPS (Very critical if your lost somewhere, has saved lives!) (Satellites.)

Long range television! (Satellites.)

Long Range Communication (Phones,Cellphones,etc.) (Satellites.)

Internet. (Satellites, and power lines of course.)

(Much much more.)

Now onto the somewhat psyhcological and green-wise part of why we need Space Exploration.

If we stopped warring with eachohter and wasting precious minerals that we have on this Earth -on- war, we would have a lot more resources to spend on more important things such as daily life, and hey, space exploration wouldnt mind some more attention either. If we spent our time looking for other planets, and other areas of expansion. We would be a much more healthy planet and society. Our Earth is also nearlly completely explored except for the oceans depths which are frankly impossible to get to the bottom too. The pressures are far far too powerful and some even say its more dangerous to trek to the bottom of our oceans then it is into space. Our bodies and steels cannot handle the intense pressure they have for more then a half hour. (The window of an exploratory sub cracked and the crew nearly died before they had to immediately go back up.)

Look at the casualties of war and the waste of resources and land. Oil spills are causing massive damage to the eco-system, the recent gulf spill has me worried that the entire balance might just be at stake. We have seen that solar powered cars can convert it to electricity and has just as much if not more power then gas cars. (Instant accelereation* and some have gone to 100 mph.)
* You have to rev your engine on a gas car to get gas into the engine before accelerating. With electricity the power is instant.

Solar Power is infinitely renewable (Until the sun dies.) and infinitely powerful, why waste money on oil rigs? Your going to get alot more money on solar power and less expenses with minor maintence.

There are so many more things I can name at this time, but here are just a few as I must go eat for now.

Space exploration entails research and development on multifarious fronts, all of which require monetary investment and a period of trial and error in innovation before any outcome, whether positive or otherwise, can manifest. An example is R&D in the pharmaceutical industry. The cost may be fairly high, but if any discoveries that benefit mankind directly or via a spillover effect are made, the advantages will be vast.

If it's being explored for the right reasons.

Okay, well, if it's being explored for useful reasons.

To put it bluntly, if aliens were discovered on the face of Mercury, wouldn't you be interested in hearing about it? I know I would.
Just as man could help but wonder if the Earth was really flat, or if there was anything outside the 'Known World'. We now feel the same about space, human kind has always needed answers, questions temp us, pull us together and satisfy us when we find the answer. The question's being asked at the moment are: 'How did the universe begin?' and 'Is there life outside of Earth?'. These questions drive so many people that calling space travel a 'waste of money' seems to be an insult to so many people's lives and careers!

There are a lot of examples for that such as the digital watch and many types of new materials.

Space exploration can lead to humanity's safety in continuance if/when space exploration have developed more efficient ways to travel. Mars has been dubbed the Earth due to it's availability to terraforming. The Safety provided of moving to Mars will give a sure securance if Earth was stuck by devastation of the cosmos.

It's pretty simple. This is were research happens. Test, trying things out. See what works. What can be improved. Patents on new innovations to create a more sustainable and efficient world.
http://en.wikipedia.org/wiki/NASA_spin-off