Pandora is specifically for this purpose. Type in Allman Brothers or any other band (or even specific song) you're into, and it'll play similar tunes by other artists. And you might create several stations of various bands/songs and 'quickmix' them all.

Otherwise, I suggest ZZ Top. I know Eliminator is prolly considered their crowning achievement, but I prefer the 70's era stuff more. The ZZ Top 6 Pack is a great buy if you find it...their 1st six albums on 3 discs. Otherwise, they're all good except for Afterburner or Recycler. And of course there's several greatest hits collections and a fairly recent compilation, "One Foot in the Blues".

Also, for a more obscure recommendation, let me suggest The Hellecasters. Pandora played them on my Eric Johnson station, as they're strictly instrumental, and of course play the 'hell' outta their Tele's. I've yet to buy their albums yet, but from what I hear on Pandora, I love 'em. Now I've made their own station there and it's my new favorite.