With the AP exam in early May and state wide tests soon thereafter, here are some review sites.
I'll add to these as I find more, but if you know some, please leave a message.
Conservapedia (what is Conservapedia?)
Government in America
Glencoe - select a unit and chapter and then do the questions
Sample Gov Examination 1, Answers
Sample Gov Examination 2, Answers
Sample Gov Examination 3, Answers
Sample Gov Examination 4, Answers
AP Teacher Made Test
Online Textbook with a great search engine for kids who are reviewing