Hmmm...prolly Pantera with Anthrax. Although spending New Year's Eve 2000 with ZZ Top here in Houston was quite an experience too. But like was already mentioned...so was that last Rush tour, they were flawless. But I've had fun at practically every concert I've been too, like a free Kenny Wayne Shepherd show down on the beach in Galveston. Maybe one of the most obscure concerts of note would be Leo Kottke.
As far as disappointments, the only ones that come to mind are Black Sabbath, and another particular ZZ Top show in the Astrodome (just cuz that place doesn't have very good acoustics).