NASA offers people the opportunity to go to Mars, albeit it being just your name that will be included on a chip aboard a new Mars Science Laboratory Rover which is due to be launched in 2011. A great initiative to get people and especially kids more interested in such projects.
You can sign up at the NASA site here, which will result in a certificate being generated with your name on it (see image below). At this point 755,294 people have signed up, which is shown on a world map with a list of the number of participants per country.
So, get going and send yourself, your kids and your pets to Mars!