Phish is alright but the String Cheese Incident is better and the Grateful Dead rules them all.

Other bands you should check out:
The Band
Love
The Thirteenth Floor Elevator
Frank Zappa and The Mothers of Invention
Big Brother and the Holding Co.
Country Joe and the Fish
Jethro Tull
moe.
Modeski Martin & Wood
Keller Williams
Yonder Mountain String Band
...to name a few

Oh and check out Porcelain Hand Jive (my buddy's band) @ Fans of the Jive