Panic is probably the preeminent jam band today with the demise of Phish, although the Panic is on a hiatus right now, I believe. decent songs but of course the real goal is to spin out of the restrictions of conventional song structure and launch into improvisational magic.
probably my favorite jam bands, tho, are Moe and Govt. Mule, although the Mule is far more heavy. their recent live cd/dvd, the Deepest End, is just incredibly amazing, with soooo many heavy hitters, among the bassists preset for a night of music that began at 10:10 p.m. and ended at 3:35 a.m. were Jack Casady, Les Claypool, Roger Glover, Will Lee, Jason Newsted, Rob Wasserman, Victor Wooten, George Porter Jr., Conrad Lozano, and a half-dozen others. Other musicians participating in the festivities -- many of whom who had gigs in the Crescent City at the same time -- include David Hidalgo, Bernie Worrell, Fred Wesley, Karl Denson, Sonny Landreth, the Dirty Dozen Brass Band horns, Béla Fleck, and Ivan Neville.