Over the course of its six seasons, HBO's Sex and the City had numerous cameos and story arc with many famous actors, and was the first show many now-famous actors appeared on. Listening to the SATC marathon this evening while I putter about the room doing other things, so far I've seen Clark Gregg (S3E12 "Don't Ask, Don't Tell"), Matthew McConaughey (S3E13 "Escape from New York"), and Vince Vaughn and the late Hugh Hefner (S314 "Sex and Another City").
I looked up to hear a familiar voice when they were showing S3E15 "Hot Chi!d in the City"; Kat makes her professional acting debut as Samantha's latest client, Jenny Brier, a 13-year-old Jewish-American princess, planning her million-dollar bat mitzvah. (Obviously she was not in any inappropriate scenes.)
That episode also featured Charlotte's husband being caught jerking off to an issue of JUGGS.