I just started watching Buffy the Vampire Slayer on Hulu and I have to say, I'm totally in love with this show! Some (okay, Most) of the characters can get annoying, but I love the bad guys! Esp. Drusilla and Spike.
Someone told me Spike gets all crappy later in the series but since I've only seen up to season 3, I have to say that he's probably my favorite!