Hmm.. Let's start with the "bigger" Netflix picks, all worth watching, but again you've probably either thought about - or have - watched these:
Lost (highly recommend)
Doctor Who
Breaking Bad
Scrubs (highly recommend, but don't watch Season 9)

And, some other (either cancelled, or less known, or newer series):
Archer
Jericho
Firefly (and the movie sequel Serenity)
Torchwood