There are several online puzzle competitons catering to reasonably advanced puzzle solvers. None have prizes.
PQRST - run by Cihan Altay
Forsmarts - run by Vladimir Portugalov
IPST (Internet Puzzle Solvers Test) - run by the Russian puzzle club Diogen
WPC (World Puzzle Championship) - run by the World Puzzle Federation
PDT (Puzzle Design Tournament) - run by Cihan Altay