hmm , well, heres the site for the whole 7 millenium questions..... u get a million if u solve any of them , but the acceptance of ur solution process is quite rigorous. Look at the P=NP problem with its minesweeper relationship(its neat). The site gives a simple description of the problem then if u click on the official question like on the right, u get the full mathematical termed problem. They are pretty neat to look at and think about.
heres the link:
http://www.claymath.org/Millennium_Prize_Problems/