Grateful Dead
Widespread Panic
Allman Brothers Band (especially with Warren and Derek)
Eric Clapton (Blind Faith, Cream, Derek and the Dominos, solo,...). Except "Wonderful Tonight"

Clash
Little Feat (with Lowell George) (Best live LP ever is "Waiting for Columbus"). Bonus points for best LP artwork, too.
Notable concerts
First ABB show: Mile High Stadium 6/23/74.
First GD show: Red Rocks 7/8/78.
Other notable GD shows: Ventura 7/30/83 (the night the lights went out in Ventura); Telluride 8/15-16/87 (too much of everything is just enough)
First WSP show: Fox Theater Boulder 1/18/96
Other notables:
The Cure Fiddler's Green 9/4/89 (Best light show ever!)
U2 Sun Devil Stadium 12/19-20/87 (last two shows of Joshua Tree tour, $5 tix)
Shows I've seen in past year or so...
Widespread Panic (RR and Broomfield Halloween)
SCI (Big Gigantic Incident at New Years)
Yonder Mountain (with beer tastings!!!)
Dispatch
Michael Franti and Spearhead/North Mississippi All Stars
The Revivalists (Thanks Dave!!!)