this is a very meaty subject...and I think it would be great to see what people have to say..
Try to keep it under 5 artists for simplicity sake...
The Allman Brothers Band
Stevie Ray Vaughan
Eric Clapton (any band or solo)
I am very young though, and really only started listening to older rock last year...my list is constantly changing, and Pink Floyd could be up there very easily as well as AC/DC who was the band that got me into older rock. And I am just now getting into Bob Dylan and Neil Young...they could make a run at that list as well.