NASA Mars mission in 2018
I know this would be absolutely best case senario, but there it is in the <a href="http://www.spaceref.com/news/viewnews.html?id=924>NASA budget:
While NASA's charts show a possible human landing on Mars in the 2020 window Isakowitz did not back away from the notion that it could happen as soon as 2018. He did emphasize that the exact course of the program is going to be based on results and that things will remain fluid for some time with regard to exact dates.
Clearly "results" means something interesting. If Mars is dry and has always been dead then I doubt we'll go before 2030. If they found fossils I expect the 2018 date would be more realistic.