Well, since we're limited to two, here they are:
Radiohead - I've seen Radiohead twice now, first at the Shoreline in Mountain View, last September. Amazing show, but when I saw them at Coachella in May, it was positively the best live show I've ever been to, absolutely incredible.
Grandaddy - I saw them in March in San Francisco at the Warfield. I've always enjoyed their music, but seeing them live was a completely different experience. The atmosphere was awesome, and they sounded better than anyone else I've ever heard live. Amazing.