1. Dave Pirner (of Soul Asylum) in Reality Bites
He is sitting on a couch behind Janeane Garafalo as she informs us that her parents "pee with the door open." He then mumbles something incoherent.

2. George Clinton (of George Clinton and the P-Funk All Stars) in PCU
After a trip to find beer and an unfortunate incident with an old woman and Pampers, Gutter cannot find a way back to campus; George shows up in the nick of time and gives him a ride on the tour bus.

3. Elvis Costello (of Elvis Costello and the Attractions and just Elvis Costello) in 200 Cigarettes
A subplot of this movie is one character's obsession with Elvis C.; he actually shows up at her party (as demonstrated in Polaroids), but she is "indisposed" and doesn't get to see him. There are also rumors that he walks between Courtney Love and Paul Rudd (recently Phoebe's boyfriend on Friends, not that I watch that show) in one scene. I need to watch again to see if this is true.

4. Eddie Vedder (of Pearl Jam) in Singles
You will find him sitting in a restaurant booth near the end of the film, playing the never-ending role of deep, introverted rocker. This movie also features cameos from the rest of the band, and performances by Alice in Chains and Soundgarden. Eddie's 'State of Love and Trust' and 'Breath' are on the soundtrack and can't be found anywhere else.

5. Alice Cooper in Wayne's World
Wayne and Garth get backstage passes to see the band; after passing hordes of groupies they arrive to take part in this conversation:
Wayne Campbell: So, do you come to Milwaukee often?
Alice Cooper: Well, I'm a regular visitor here, but Milwaukee has certainly had its share of visitors. The French missionaries and explorers began visiting here in the late 16th century.
Pete (band member): Hey, isn't "Milwaukee" an Indian name?
Alice Cooper: Yes, Pete, it is. In fact, it's pronounced "mill-e-wah-que" which is Algonquin for "the good land."
Wayne Campbell: I was not aware of that.