I recommend Season 1 and the last half of Season 3 of Heroes. Season 2 started out alright, but due to the writer's strike and some truly shitty writing, quickly degenerated into absolute trash until midway through Season 3. The last half of Season 3 started to see some of the old first season magic of Heroes back again since a few of the writers from Season 1 came back on board, even though a lot of it was retconning and fixing the fuck-ups of Season 2-3.5.
I'd recommend checking out Sanctuary (13 episode show so far that was born from a webcast, believe it not, due to come back for Season 2 soon). I'd also recommend Fringe -- it got a bit lackluster towards the middle of the season, but they went out so goddamn strong in the season finale that I'm actually itching for the new season to start up again.
Also, if you can get through the first Fox-run episodes of Dollhouse, which is Joss Whedon's new baby, the last 7 episodes of the first season are asskickingly good. If you're a fan of Whedon's work, you'll get to see a lot of old faces from Buffy and Firefly, and who doesn't like a little Helo in their day?