Mystik Spiral is Trent's alternative and anarchist band. Its music isn't particularly good, and it's anarchist tendencies consist mainly of spray-painting anarchy signs on the Tank (a very abused thing that "used to be a van") and various other items. Still, the lyrics are pretty interesting, its members seem to get about as enthusiastic about it as they can (i.e. actually wake up for practice ocasionally), and the show definitely wouldn't be the same if not for "The Spiral".
Mystik Spiral has had a few gigs over the episodes, and they play every Sunday night at McGrundy's Pub.
It is an ongoing joke in the show that Trent wants to change the Spiral's name in some way, which he thinks will somehow help the band in it's search for "the big break".
Besides Trent, the lead singer, and Jesse, the lead guitarist, there's also Max Tyler, the drummer, and Nick Campbell, who plays bass guitar.
Behind My Eyelids
Mystik Spiral's picture was taken from The Misery Chick (the website, not the episode).
Songs
Icebox Woman
Every Dog Has Its Day
Betrayal
Frickin' Friends
(There are more. I'll put them up as soon as I have the presence to remember them. Of course, you can send them here and I'll get them up faster...)