I've been to a few historic events, an ALMS race at Limerock, an IndyCar race at Watkins Glen, and the '04 USGP, but nothing compared to the 2011 Indy 500 for me.
No especially notable drivers, but when you're in the 3rd row at the turn in for T1, your bones shake as the field runs into T1 for the first time (I was literally shaking). Then, lap after lap, rubber is spit in your face and air slammed, very loudly, into your ear, in a way that seems simply unachievable. Of course, being the 100th Anniversary and all, there was a lot of history surrounding the event, and no doubt that the race itself was going to be a classic.