I believe the most site that has freerolls is
full tilt poker. They practically have one every hour or ever other hour. There freerolls range from NL holdem, HORSE, RAZZ, OMAHA. They max at 2700 entrants and it can get full quick, ususally within the first two minutes of registration open. The freerolls are $100 and they pay top 27 players. I personally have a few of their freerolls, which first pays out $15.
Other freeroll sites to try out is Players Only. They have $1000 freerolls and satellite freerolls to their million tourney. Also another site to try out is
bodog poker, they have $500 daily freerolls at least 2 or 3 times a day.