When I was doing Forget-Me-Not Lane at the Taper, we always had incredible people backstage - I met Groucho, Steve Allen and Jayne Meadows, Christopher Isherwood and Don Bachardy, Elsa Lanchester (the latter three people I saw many times over the next year, as I brunched regularly at Elsa's beach house, which was next door to the Isherwood/Bachardy house), Ray Bradbury, Julie Harris, and many, many others.
I loved meeting Rosemary Harris when I went backstage to see Crista Moore - I almost convinced her to sing Send In The Clowns on the Sondheim album. Marian Seldes was a treat, too.