I had a bit of a chuckle the other night when I watched 4 episodes of Murder, She Wrote with 4 guests from 4 different Star Trek series. Kate Mulgrew, Rene Auberjonois, Levar Burton and George Takei. I believe all of the episodes are in season 3. The episode with Levar Burton also had Ernest Borgnine(sounds like a Trekish name, eh?) and Adam West!
Mulgrew showed up twice (as different characters- one of them in one of the Cabot Cove episodes) Robbie McNeill showed up as well. I think Jeri Ryan did too Robert Beltran played a murder victim on one.
Going back even further ... try doing it with "Gunsmoke." With its 20 year run quite a few Trek actors worked on it. It even seems as though I've been able to spot at least one per episode - of course that includes actors who guest-starred on Trek and not just series regulars (though Nimoy made several villianous appearances).
Oh, trust me, I know Gargoyles! In fact, I love Jonathan Frakes more for being Xanatos than Riker. I always wondered why Patrick Stewart was never on Gargoyles...
And, of course, there was a mini Trek reunion on T.J. Hooker: [yt]https://www.youtube.com/watch?v=uFel8BReseY[/yt]
I watched an episode of NCIS last weekend that had both Connor Trineer and Tim Russ in it. They didn't have a scene together though, that would have been cool.
House M.D. had Mayweather and T'Pol from Enterprise and nuSulu (different episodes though). And probably others that I don't recall.
Or check out the prequal meeting of Nimoy and Shatner from The Man from UNCLE (a brilliantly great TV series as well). Both Harlan Ellison and James Doohan worked on this series. http://youtu.be/8_5nAI1vnpc (sorry, I am unaware as to how to display the clip in similiar fashion as to the one above).
Speaking of The Man from UNCLE, I just saw an episode with Susan Oliver, Antoinette Bower, Reggie Nalder, and TOS bit players Tom Troupe and George Sawaya.