I always love seeing awesome bands doing cameos in movies. Why them? Who did they know to put them in? Either way it's great.
1) Primus in Bill and Ted's Bogus Journey
2) Ozomatli in Never Been Kissed
3) Infectious Grooves in Encino Man
4) Gwar as Ministry in Hardware
5) Morris Day and The Time in Jay and Silent Bob Strike Back
Honorable mentions to Twisted Sister in Pee-Wee's Big Adventure and Oingo Boingo in Back To School
Hahahaha amended. I totally forgot about the Red Hot Chili Peppers in Tough Guys. Thanks Brandon.