My Morning Jacket - one of today's best live bands
Kings of Leon - I don't love 'em, but they put on a good show and college kids seem to worship them
white Stripes - Jack and Edge are buddies
Fleet Foxes
MIA
wilco
Muse
Insane Clown Posse
Pearl Jam might be too big to be an opener, generally, but I could see them doing one night in Seattle or somewhere. Also, maybe even have people like Patti Smith, Leonard Cohen, Pixies, Public Enemy, etc. do special one-show appearances. Probably not gonna happen, but a girl can dream.
(Also, best U2 opener for me was, hands down, PJ Harvey. Stories from the City/Stories from the Sea songs live
)