I'm surprised that no one has mentioned Boston yet - they're one of the best groups to ever play, I think. Tom Scholz 's technical mastery and Brad Delp's voice just combine for something great.
Some of these guys have already been mentioned, but some other really good bands that I like are ZZ Top, The Cars, BTO, CCR, Foreigner, Dire Straits, ELO, Aerosmith, John Mellencamp, RTZ, The Travelling Wilburys, Huey Lewis & The News, Tom Petty, Eddie Money, Asia, The Beatles, and Bob Seger.
There are probably more, but those are the ones that come to mind at the moment.