Ace links to a list: "20 Real-Cool Fake Bands from TV and Movies." The sad thing is that they included some really lame bands, and forgot several excellent ones.
First, as Ace points out, Eddie and the Cruisers didn't even make the list. Whiskey Tango Foxtrot!?
Other great movie groups they missed:
-Wyld Styllyns (Bill and Ted's Excellent Adventure)
-the Blues Brothers
-the Monkees (ok, they're TV)
-The Wonders (That Thing You Do)
-The Lone Rangers (Airheads)
-Suburban Funk (The New Guy)
-James "Thunder" Early and the Dreamettes (Dreamgirls)
... and my all-time personal favorite: The Commitments, from the movie of the same name.