Paul Davies makes an interesting case for a realistic mission to Mars: Make it a one-way trip (NYT registration required).

It wouldn't be the first time explorers have gone on to new lands without expectation of coming back, and the potential gain is significant. Unlike the Moon, Mars can provide a sustainable habitat, with minimal supplies sent from Earth each time the 2.2-year window opens up.

Further, if we start with a crew of four, and add more people as the colony proves its viability, then this concept starts to look less and less like a suicide mission, and more like colonization.

Sure, there are tons of problems, not the least of which is that so far 20 of the 36 craft sent to Mars have failed en-route, which makes gambling on the bi-annual resupply from Earth a harrowing and possibly deadly game, but improving the reliability of the one-way trips is infinitely easier than trying to engineer a round-trip with current technologies.