Here are a few compiled from a couple of books I'm reading at the moment (Auslander's Performing Glam Rock and Unterberger's Eight Miles High: Folk Rock's Flight from Haight-Ashbury to Woodstock):
I knew that Marc Bolan had Jewish roots, but I didn't know David Bowie's mom was Jewish, which by some standards makes him a full-fledged non-practicing member of the tribe (moreso than me, in any case, since it's matrilineal, not patrilineal). Jewish bragging rights for yet another entertainment genre!
Christina Applegate's mom, Nancy Priddy, was involved in the early folk-rock scene, inspired a Buffalo Springfield-era Stephen Stills song "Pretty Girl Why" (with which I'm unfamiliar), and sang backup on Leonard Cohen's first album.
Before her first solo album, Joni Mitchell did a bunch of demos in Chicago with an electric blues band backing her up. These are as yet unreleased.