This isn't comprehensive by any means to feel free to include your own favorites in the comments! Also there are a few, like Disney/Nick kids who got their starts on TV shows, that I'm not including because it's not really surprising that they've gone back into acting.
Lead singer of Bush and Gwen Stefani's ex Gavin Rosdale started out with small roles in Zoolander and Little Black Book, but really broke out as an actor in the 2004 film Constantine starring Keanu Reeves. He's had a few roles since, mostly on TV, but nothing major.
Before her tragic death, Aaliyah was becoming quite an actress. She starred in Romeo Must Die, had finished filming Queen of the Damned (although her brother had to finish some of the overdubs), and was set to star in Honey as the title character, who was instead played by Jessica Alba.
This video quality is bad, but has bonus DMX!
Beyoncé is rumored to have a picture of an Oscar in front of her treadmill as motivation. Whether that's true or not she's certainly given it the old college try with acting. Beginning in 2001 with Carmen: A Hip Hopera, making her way into comedies with Austin Powers in Goldmember and The Pink Panther, being nominated for a Golden Globe for Dreamgirls, and now voicing Nala in Disney's live-action version of The Lion King, she's no stranger to the screen.
Although she was technically billed as a supporting actress, Jennifer Hudson was the breakout star of Dreamgirls. She won a Golden Globe, BAFTA, and an Oscar for her portrayal of Effie White. She's had minor roles since then in both movies and on TV.
I know "And I'm Telling You I'm Not Going" is the quintessential song from the part but I love this one.
When you look like a creep you might as well play one on TV, and Marilyn Manson has put his looks and personality to good use by playing weirdos. He had a recurring role on Sons of Anarchy as an imprisoned leader of the Aryan Brotherhood where he got to have swastika tattoos and say the n word.
This was never a hit and even my old ass didn't remember it from 1992, but I'm including it just because the trailer is so awesome. Mick Jagger plays a mercenary (lol) in the dystopian hellhole of 2009.
Honorable mentions for cameos:
Anthony Kiedis as an asshole surfer in Point Bread
Ric Ocasek in Hairspray (which also starred Sonny Bono, Debbie Harry and Vitamin C)
Also the whole reason for this post is that Kevin Ray, bass player for Walk the Moon, will be guesting on Elementary on Monday night. Kevin recently moved from Indianapolis to LA, so I wouldn't be shocked if he does more acting in the future. Here's a preview of his scene that I can't get to embed, but check it out!
Sources: Gavin Rosdale | Aaliyah | Beyoncé | Jennifer Hudson | Marilyn Manson | Mick Jagger | Anthony Kiedis | Ric Ocasek
Big thank you to judasiscariotbluecidxtinkerbellaxbeysactingcoachvibeology_eshittysoupmilfordacademy and thankyounotes for helping me with ideas!
Have a great weekend ONTD!