There's always the option of going onto YouTube and looking up every song because all the Rock Band tracks are there somewhere.
But if you are interested in songs you've heard before, these are the hits:
RED HOT CHILI PEPPERS
Under the Bridge
Breaking the Girl
Suck My Kiss
(Note that Give It Away isn't available to download)
Here Comes Your Man
Monkey Gone to Heaven
Just What I Needed
My Best Friend's Girl
Good Times Roll
(Moving In Stereo, while not a hit, was the song used in Fast Times at Ridgemont High for the famous Phoebe Cates pool scene)
I downloaded the entire pack of The Who even though I didn't know half the songs. You'd probably know Baby O'Reilly and Who Are You (the CSI: NY and CSI theme songs) and Summertime Blues.
If you haven't gotten it already, in my opinion the Boston pack is the best one of them all.