Newer Stuff:

Flogging Molly is absolutely awesome. It kinda punk-flavored irish, or vice versa, but its some really good stuff. Start with the album "Drunken Lullabies" and if you like that check out "Within a Mile of Home" or "Swagger".

Street Dogs are like them, but more punk. Their lead singer is the guy who founded Dropkick Murphys.

VHS or Beta is pretty cool - the album is "Bring on the Commets" - kinda pop-rock like the Killers, but I think a little better.

Older:
+1 about CCR - the Movie Album is a pretty good sampler, but its hard to go wrong with Credence.

Talking Heads - amazing. "Stop Making Sense" is a great album, and better concert DVD.

Van Morrison, I can't say enough good things about. Astral Weeks and Moondance are his first/best known albums, but he's been recording since then and goes through a variety of styles. DEFINITELY not for everyone, but if you want more specifics on his stuff, I'm happy to provide.

Thin Lizzy - they were contemporaries of Zepplin and Aerosmith and whatnot, but seemingly haven't gotten the attention they desrve beyond one or two hits. They have a live cd - "Live and Dangerous" I think its called, that is purely awesome.

The Band - basically the fathers of rock - amazing shit.

Those're a few to start with. If you like any I can provide more.