Newgrounds
Newgrounds... what can be said for the creator; Mr. Fulp and company? They are the ones that made flash so successful (IMO). Millions of games, tons of sites, free animated shorts.
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XGen Studios

Free Games... great for causal gamers.
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Update: Canyon Defense is now kinda old, look for something else on their website. Original statement: Check out their content, I really like their Canyon Defense game.