There are a number of online programming contests of interest to Haskell programmers. This page attempts to document and help coordinate the efforts of the Haskell community.
The ICFP Programming Contest
A yearly contest run by the functional programming community, open to all comers. Haskell has been highly successful over the years, winning several times.
Great Language Shootout
A highly visible language performance contest.
The old wiki keeps a track of our submissions.
"Project Euler is a series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve."
International Obfuscated Haskell Code Contest
The IOHCC as been held three times.