Hey just found this old but great thread! I recently realised how great title sequences some tv series have - or at least used to have. Nowadays they keep them as short as possible, sometimes only briefly flashing the title and "Created by" and then the rest appear on the screen when the episode is already running. Anyway here are some of my favorites:
Twin Peaks http://www.youtube.com/watch?v=7oDuGN6K3VQProbably the best opening sequence for any show. Puts you just in the right mood. God, I liked the series overall, too!
The Sopranos http://www.youtube.com/watch?v=NUT07eZoXPwThe only possible contender for Twin Peaks. I can't imagine ever skipping it.
The X-Files http://www.youtube.com/watch?v=3YIzX4r-sF0&feature=relatedNever really watched the series but the opening sequence is great.
South Park http://www.youtube.com/watch?v=6268nvdiqso&feature=relatedPlain genious!
Hill Street Blues I can't find a good version of the opening on YouTube.
Deadwood http://www.youtube.com/watch?v=B909njPoX7kBonanza http://www.youtube.com/watch?v=cTWB_ByQD4wI wouldn't call it the best ever but it's classic anyway and you can't get the tune out of your head once you've heard it.
Monty Python's Flying Circus (all of them)
http://www.youtube.com/watch?v=Tq37WSg9ESgNo explanations needed. The thing got a bit out of hand on the latter seasons where the titles could appear 20 minutes into the show, fastforwarded or possible not appear at all. And then there's the whole business with the ending credits!