The 4 sites I play:888 - several.... - blast freerolls, freerolls in restricted tournament section, poker club as you move levels, monthly such as FB twitter, instagram, etc.
Pokerstars - CC freerolls, periodic good promotions, school passes
ACR - freerolls gone for now, probably coming back soon
PP - not many freerolls, but great lowest cost .02 to .11 options to win tickets pretty easy worth 11x value (.22, .44, 1.10).