All my Dad ever took me to was sprint cars at Ascot (and one Nascar? race at the old Riverside Raceway). Sprint cars and karts are both awesome to watch (I heard the best karts lap Laguna Seca quicker than the Nascar cars!).
For pure racing thrills I like motorcycles. The big dirt track bikes on one mile ovals (like at Del Mar ) make for pretty harry racing. AMA road racing,too, of course.
But I just can't stomach NASCAR and their takeover of the programming on Speed. Always used to be some good racing on there, now it's all about Nascar.