My favorite thus far was actually a 3-group performance. Lifehouse was the headliner - they were opened by Matt Nathanson, who was opened by Honeyhoney. I actually thought Matt had a better live performance than Lifehouse. Honeyhoney is a small, no-name group, but they're pretty good. All three groups are on iTunes, check 'em out.
I saw the Eagles this summer. They were phenomenal, but the concert was 3.5 hours long. Still, the best was saved for last - Take It Easy and Desperado
Styx, Switchfoot, and Kansas all put on decent shows. I wouldn't need to see them again, but they were cool. Boys Like Girls is coming to my college soon. I'm not crazy-nuts about them, but I think they're good enough that I ought to go.
I'm jealous of whoever is going to see Brad Paisley, and whoever's seen Counting Crows.