^Yeah, i knew several Housewives veterans were on Trek. Thanks for those.
Culp did show up in Enterprise as well, but I don't recall if that was before or after his Desperate Housewives stint. Mark Moses from that show was Jonathan Archer's dad as well, in 'Broken Bow'.
I'm going to go off-topic, but it's related to the DH-ST connection. I read an interview with Felicity Huffman, Lynette in DH, where she said that she auditioned for a role in Trek but was turned down. I got the impression it was as a regular. The only ones I can think of that she might have suited would (and which fit time-wise) be Janeway or Kira.
Technically, Steven Culp doesn't meet the title criteria - before doing NEM or ENT, he had played RFK in the movie 13 Days (opposite the new Captain Pike, Bruce Greenwood, who played JFK) and he was in the West Wing.
Most of the big names - Alley, Hatcher, Dunst, Jansen, Collins - have already been mentioned. Of course, the thread also depends on what you mean by 'celebs.' Actors like Penny Jonson Gerald or Gregory Itzin were in Trek before becoming more recognisable in 24; ditto Michelle Forbes and Homicide. Bill Campbell was in TNG as The Outrageous Okuna before starring in The Rocketeer and The 4400. But are any of them celebs?
You could say that Colm Meaney meets the criteria. He was a recurring, nameless character in TNG for some time, before becoming famous in movies like The Commitments or Far And Away, then his character became Chief O'Brien, obviously becoming one of modern Trek's best loved characters. Even Alexander Siddig is arguably better known for his post-Trek work - roles in Syriana, 24 and Spooks (MI5 as it's called in the US) have brought him to a wider audience than DS9 ever did.
There's also Clint Howard, brother of Ron. Not really a celeb, but he's quite recognisable through his cameo's in all of little bro's movies. He played Balok in TOS' Corbomite Maneouvre, then would go on to star in Gentle Ben. He also turned up in ENT as a Ferengi.