I've been to many, but just to name a few:

-Slipknot (jaegermeister tour)
-311 (many times, but 10th anniversary show was amazing)
-Avenged Sevenfold (seen them twice already, but next saturday's show should trump all others)
-First year of Family Values Tour (Incubus, Orgy, Limp Bizkit, Rammstein, Korn).

I'll be seeing Children of Bodom and Trivium together in november. :D