Here's a couple prize items from the Mars Society:
2011 Mars Society Poster Contest - The winner will help publicize this year's International Mars Society Convention, which will be held in Dallas.
Meet the Competitors - The competitors in this year's University Rover Challenge have been selected, and are now listed on the URC 2011 Teams page. There are links to web sites for most of the teams there, so it's easy to learn more about them.
One of the University Rover Challenge competitors, the University of Michigan Mars Rover Team, has its own space prize, the 2011 Mars Rover High School Contest for Michigan high school teams. The first place prize is $600, there is a total of $1000 in prizes.