Surfthechannel.com is a good one. It uses Megavideo though, so you won't be able to watch the full episodes in one sitting unless you're a member. You'll have to watch 25 minutes, wait about an hour, then watch the other half of it.
It really pisses me off because I used to use it to watch Dexter.
Hulu is also good for watching Heroes.
Seasons 2 and 3 both almost made me stop watching. The recent episodes (should be Season 4, but I guess is Season 3: Part Two) have been outstanding.
Heroes will always be my #4 show though. Behind RAW, well behind Entourage, and nowhere even close to the ballpark of Dexter.
The second half of Heroes S3 has been pretty damn great. Season 2 was worse. There was one amazing ep in S3 tho with the Haitian and Peter going to Arthur.
Dexter fucking owns, tho DOAKES is missed . Still miss him ;_:. Thought S1 was absolute tv gold as was S 2. S3 wasn't quite as good imo.