There are plenty of sites to keep a freerolling poker player busy. The one they choose depends on personal preference. And noone said you are by any means restricted to just one site for online freerolling, anyone can enter as many or as little as they like.

Here are a few popular ones to name.

Full Tilt Poker
Sportsbook Poker
Doyles Room
PDC Poker
Titan Poker
Absolute Poker

There are many, many more, but heres a few to get your feet wet.