I addition to many of the great recommendations above, also consider:
Dave Matthews & Tim Reynolds Live at Luther College
Hot Tuna, recorded live at the new orleans house, berkeley 1969
Rory Gallagher, BBC Sessions
Bruce Hornsby, Here Come the Noise Makers
Joe Bonamassa, A New Day Yesterday Live
Its hard to pick a 'Best' live album. Hot Tuna is excellent when I'm in a more laid back mood. This is an acoustic set recorded in a small club atmosphere. When I want something with raw energy, Joe Bonamassa, A New Day Yesterday Live never fails.