There are several known star Trek lookalike artists around the world, some, granted, are not actors, but many could and have played their respective roles on screen.
While I love shows like Hidden Frontier which feature brand new characters, it's always fun every once in a while to catch up with old friends. I have decided to leave out the regular casts of New Voyages/Phase II and Star Trek Continues
Here are just a few:
Jeff Trusk as [older] Captain Kirk - http://www.jtrusk.com/
- quite well-known, has made a few TV appearances including Jay Len's Tonight Show alongside Shatner himself. Was mooted to appear as Kirk's father in a German film based on Diane Carey's 'Final Frontier, but the project seems to have been abandoned
'Vulcan Willi' - http://www.der-deutsche-spock.de/index_en.htm
- German Ninoy lookalike; played Spock in the abandined 'Das Vermachtnis' fanfilm, plus Borgwar3: Atlantis as another Vulcan captain in 1998
Spock Vegas - http://www.gigsalad.com/spock_vegas_las_vegas
- Dunno if he can act but he is very tall and the resemblance is definitely there.
Carl Sheldon as [older] Scotty - www.youtube.com/user/einstein8395
- breaking my rule slightly, Carl will be appearing in Phase II: The Holiest Thing.
Giles Aston as Jean-Luc Picard - www.jeanlucpicard.com/
- played the part in Star Trek: Intrepid's upcoming 'The Stone Unturned' and another... 'parody'. He also works with Barron Toller as Sisko
Clynell Jackson as Ben Sisko - http://www.hiddenfrontier.com/episodes/ODY300.php
- not a lookalike as such, but he gave a very good portrayal in Star Trek: Odyssey.
- this has a few people including Seven of Nine.
There's bound to be more out there, I've seen cosplayers do good Data and Worf