Elon Musk, he of PayPal, SpaceX, and Tesla Motors, has always said he wants to put humans on Mars. Recently, he gave a few details of how he intends to do that.
First, he says, we need fully reusable rocket launchers and spacecraft, to cut the cost of going into space to a reasonable amount for individuals. SpaceX is already working on that technology, and Musk is currently pegging the price for a ticket to Mars at around $500,000. He envisions building a colony on Mars, starting with fewer than 10 people, but growing to perhaps 80,000, gaining self-sufficiency along the way.