The Deadliest CatchOne of the few instances of "appointment television" that still interests me. M and I have been hooked since it started.
Coincidentally, the only other two shows that we bother to keep up with are running now too. A new season of South Park started a few weeks ago and the last eight episodes of The Sopranos starts this Sunday. We still love Mythbusters, but we don't actually make it a goal to catch them when they're new.