I've met Teresa Graves; she was in England for a while in the '70's and she knew my family - my dad gets a name check in her Awake article. She also appeared in a cheesy Vampire movie with David Niven. She was (when I visited the US with my family in the '80's) married to a bus driver in a Beverley Hills cong.
Michael Jackson visited my cong in London the early '80's. Yes he did come in a limo, yes, he did dress funny, though not the full whack job monty, and yes, he did go on field service.
Hank Marvin from the Shadows (early backing group for Cliff Richard, 'successful' in their own right with their own blend of anodyne twangy guitar lead instrumentals) is an elder, or at least was when he moved to Oz a few years ago. Cliff Richard is rumoured to have been unable to reconcile his (allegedy non-consumated) homosexuality with the JW's stance on it.
Geri Halliwell was indeed bought up a Witness. And boy, does she need to be educated about the effects of growing up in a cult or what?
Larry Graham and George Benson have been JW's although I don't know their current status. I think Graham is the 'ultimate' former celeb Witness, as he networks like crazy, thus Prince's current daliance (but is he baptised, I think not).
Patti Smith's parents are Witnesses.
Chrissie Hynde studied with a pioneer I knew. She's a vegetarian who likes Boxing, and is into Buddism. Yes, well...
I spent three hours talking to either Stock or Aitken when 'on the doors' in Little Venice in London in the mid '80's (of Stock, Aitken and Waterman, purveyors of Eurodisco/Hi-NRG crap, who gave us such luminaries as Rick Astley... but then again, there's Kylie (...Kylie... Kylie... mmmmm... ).
A guy called Chris Ivy (singer in obscure '70's/'80's disco band called USA) was an elder in a London congregation until he was df'd; I don't know his current status.
The song 'Pray to Jehovah Each Day' (if that's the correct title) was written by a celeb Witness; possibly Graham or Benson, as the voice on the demo I've heard (where the word 'Talk' substitutes 'Pray') is almost certainly a black guy.
I reckon we should start some fun rumours; Marilyn Manson is studying, Bootsy Collins is an elder, you know, that sort of stuff.