I'm a NASCAR guy myself. Been to quite a few races, met a couple of different drivers. For some bumping, banging, and (usually) close finishes, it's a fun sport to watch. I try to catch the F1 races, but it's a little more difficult to see them all being from the states. Enjoyable nonetheless. The technology is very interesting. What new and crazy, yet successful designs the engineers come up with draws me in. I can't help but watch the Australian V8 Supercars whenever they happen to come on SPEED Channel. Those guys aren't afraid to trade some paint.
Other than that, I don't follow too many other series. I do have SPEED Channel on a decent amount of the time, though. So I do get exposure to Sprint Cars, DTM, BTCC, WTCC, ALMS, LeMans, etc... And I can never find the right channel for the Indy Car Series, other than the 500. They can occasionally be fun to watch, too.