I get emails from 888
about freerolls there, but you have to (I think) have deposited to be eligible. I dont play them cause I used to play on like 8 different sites, now I only play at one - stars. And there are often lots of entrants, so the time factor vs value is minimal. But probably a decent deal, if you have the time and dont mind freerolls.
And what Eziekiel said, check stuff out ahead of time. Plus, things change all the time, so you just kinda have to keep web-searching.
If you play a lot or just really enjoy playing, then get involved here in the forum and become a member of the freeroll club.. There are requirements - read Rules and FAQs - , but they are easy to meet if you are a poker player who likes learning. The freerolls are great value and not (quite) as donkish as normal ones..... :-)