Below is a list of the 5 biggest Stock Market Game cash prize competitions on the web. There are bigger prizes for other financial securities such as forex and ill make a list of them soon.
Hargreaves Lansdown - runs a tournament called the Big Deal Stock Market Challenge with a £10,000 cash prize once in a while.
ASX - $2000AUD per season
Investfly - $1000USD per month
Wallstreet Survivor - $500 per tournament
HowTheMarketWorks $500 per month