I'd have to put the Grateful Dead up there, too. This is based, as much as anything else, on the marvelous, impromptu, extended acoustic jam of "Scarlet Begonias" that a number of us did late in the night at a New Year's party earlier this month. I think the "homes and gathering places" criteria set above by Mark Clark is nicely met by many Grateful Dead tunes--I don't know of a single time in an informal circle at a party or other gathering that jamming on a Dead tune doesn't draw more attention of other gatherers than most contemporary music, and the rhythms are fun for nonmusical folks to grab a shaker or rainstick and join in the vibe. The Dead being more of a live band than a studio band (the greatness of "Workingman's Dead" and "American Beauty" notwithstanding), so their work translates nicely to the non-professional, non-studio setting of the common living room.

Chris