Here are some favorites:
This one has hundreds of games, resources, audio files and tests you can take yourself, and it is free:
http://www.tolearnfrench.com/
This one has a 30 free trial period:
http://www.quia.com/shared/french/
Another paying site, that published the materials I use with the 5th grade. They have great games, with trial period use available:
http://www.tribecalanguage.com/
Another with games and great audio files, also free:
http://www.bbc.co.uk/schools/primaryfrench/index_flash.shtml
For quizzes in particular topics:
http://fog.ccsf.cc.ca.us/~creitan/grammar.htm
