A lot of the best jam bands and progressive rock bands are hardly known to people who aren't already really into these genres. And it's unfortunate because much of this music is some of the best contemporary rock music around, taking over where 60's psychedelic rock left off.
So here are just two songs by one band that I guarantee you'll like assuming you have ears, just make sure to listen to the whole songs.
YouTube - Umphrey's McGee - Glory - 11/3/2006
YouTube - Umphreys McGee JaJunk JITD 2005