I saw the Foo Fighters at Lollapalooza back in August. Pretty awesome hearing everyone singing My Hero in the pouring rain. I was soaked after Sunday.http://www.youtube.com/watch?v=0b7f0FqFyLA
As for some other random suggestions:
Thrice (my current avatar) - They just put out a new album called Major/Minor which is decent. Their last album, Beggars, still my favorite. Sort of an alternative rock band that can get a little heavier at times.
The Naked & Famous - An indie rock/electropop band from New Zealand that I knew nothing about before seeing them at Lolla. Have been semi-obsessed with them since and I am seeing them next Monday at the Henry Fonda Theare.
The Horrible Crowes - If you know The Gaslight Anthem, who I also highly recommend, this is the side project of the leader singer. A little "lighter" version of The Gaslight Anthem. I saw them last month at Troubadour and it was pretty good.