Bruce Springsteen's E Street Band, especially right now, is phenomenal. I was skeptical after all the hype, but yeah, they're one of the best I've seen. I'd probably throw in Soundgarden and the Pixies too (first saw them opening for u2, one of the best opening acts I've ever seen: http://www.ranker.com/list/be...
There are just too, too many great American rock bands to pick just one. KISS, Jefferson Airplane/Starship, Grateful Dead, and ZZ Top first come to mind.
Even though they're grunge^
The list goes on and on