I have a buddy who's a flagman for the F2000 Series. When I can attend one of their races (looks like Lime Rock and Watkins Glen this year) he gets me trackside access. Aside from that, though, I'm on my own.
I shot the Toyota Grand Prix of Long Beach last year, and purchased a "photo ticket". I'm not sure if I would do it again, but I did manage to get some decent shots:
I'm heading to Daytona at the end of January for the Rolex 24. I shot it last year, so I know what I'm in for, but I still managed to get decent shots from beyond the fence:
If Daytona sold a "photo ticket", I'd probably buy it. As it is, though, a small footstool can get your point of view above the fence...