A couple more:
- Henry Rollins was in 'Lost Highway' and was also the presenter of the TV show 'Night Visions'.
- Ice T was in 'Leprechaun in the Hood'. I know, Ice T is mainly a rapper, but he was the leadsinger of the metal band Body Count too.
- Megadeth had a song featured in 'Demon Knight' (Diadems)
- Armored Saint (Great band with John Bush, now leadsinger of Anthrax) appears on stage in 'Hellraiser III - Hell on Earth'

She's not really a "rocker" but she "was" in the music business..Alliah(sp?) in Queen of the Damned..Not too bad of a movie I've seen worse..not enough gore for me though.

One more: Glenn Danzig (from 'Danzig', 'The Misfits' and 'Samhain') had a small role in 'The Prophecy II' as Samayel.

Alice Cooper in "Monster Dog" (my avatar)
Debra Harry in "Tales from the darkside the movie"
david bowie in "the hunger"

I want to name more but I want to post some more before heading to bed..

Wow! Those are all great examples! Thanks for all the info. I really have to find Trick or Treat!I was wondering how come Danzig and The Misfits aren't in more horror movies. Oh! I just remembered Marilyn Manson and The Donnas are in Jawbreaker, but that's more of an ironic high school murder movie than horror really.
Also of course The Dickies song for Killer Klowns as well as The Cramps on The Return of the Living Dead soundtrack.

Just remembered that Marilyn Manson did a song for the Spawn movie(more of a sc-fi action movie though)

marilyn manson was also in the movie "lost highway" for like a split second.. sorry if someone already mentioned this, I didnt really read all the posts on this thread.. trying to catch up on all the other threads...

henry rollins also had a small part in the crow, as did my life with the thrill kill kult. great flick. a bit overplayed but great none the less.

I had for gotten about thrill kill kult being in it.. great fucking soundtrack as well..

The Offspring in Idle Hands. Love when Dexter Holland gets top of his skull ripped up