Buffy and Angel used to be my main downloads (now just waiting on Angel season 5 to be released on DVD) and I know that when the new series of Doctor Who starts, I'll be madly trying to get the episodes as soon as possible.
The lovely Sharon and myself have seen up to episode 10 of Lost. It's created by JJ Abrams (Alias) and is about a plane-load of people who crashland on a remote - and mysterious - tropical island. The character interactions are well scripted and keep the show moving along at a reasonable pace. Most episodes give you the backstory to a character, with most backstories containing a slight twist.
The island itself contains twists, featuring creatures that are... unlikely... to be native. Locke, one of the characters with a clever backstory, comments at one point that the island gives you what you need. My one concern is that the few interviews I've read with the production team suggest that they don't actually know what's behind the mysterious things that happen on the island. That's a worry simply from the fact that X-Files didn't have any set backstory behind its conspiracy idea either, and that ended up hamstringing the show as we got increasing contradictory things happening and desperate attempts to explain away things. Hopefully Lost will avoid this.
Lost starts screening in February in Australia.
I've only seen the first episode of Carnivale, but it was... interesting. Set during the 1930's it follows a travelling side/freak show with several interesting characters. Well written with hints of things to come, it doesn't give you everything up front and leaves several unanswered questions. It's also got a few actors that I'm fond of - Clancy Brown, Micheal J. Anderson, Adrienne Barbeau.
It's currently showing on the ABC on Sunday nights here in Aus. They are tending to stick two episodes together into a movie length feature each week, meaning that we're halfway through the 12 episodes of first season already. I don't know how it'll go starting off halfway through, but I'd recommend giving it a go.