Well, I am assuming you mean "fun" bad movies as a few mentioned here were intentional spoofs and, for in my opinion, quite clever (Doc Savage, They Live, Death Race).
In that vein,
Starcrash (actually bad bad but funny as hell)
Teenagers from Outer Space
Faster Pussycat Kill Kill
Killer Klowns from Outer Space
Joysticks
Hercules in New York
It's Alive 1-3
Attack of the Mushroom People
Zardoz
Deadly Spawn
Liquid Sky (may have suffered in the kiche dept in 20+years)
The 5000 Fingers of Dr T
Alligator
Night of the Creeps
The Specials
Chopping Mall
Doc
Edit: Forgot They Saved Hitler's Brain- Tough wait for the belly laughs. They saved the whole head and it yells orders in German. JUst awesome.