I would definitely take a look at Poker.com for their freerolls. They are every 3 hours and are $100. Almost every site has freerolls but many requite you to deposit before you can claim the money if you win a freeroll. Poker.com is not one of those places, you win and its yours.
I also like the ones at interpoker that you can play once you have aqcuired enough player points. They are gauranteed $ tournaments and they are restricted in the number of players that can enter. So you stand a good chance of getting in the money.