There's most famously Hugh Laurie in House but also Jake Weber in Medium, Linus Roache in Law & Order, Damien Lewis in Life, Jonny Lee Miller in Eli Stone. And those are just the ones I watch and know about because I've tracked all of their pre-America careers.
There was also another Trainspotting alum, Kevin McKidd in the short lived Journeyman (I guess famous from Rome which I never saw). Jack Davenport is in that summer filler Swingtown. Rufus Sewell is going to be in an American remake of a British show (that originally starred Patrick Stewart) called Eleventh Hour. Oddly that was one British show I didn't like, despite Patrick.
In addition, of course, there's the other British remake of Life on Mars which I liked until the ending--wonder what they'll do about that...
Again, I think there are some others that I'm not remembering. Strange to have actors I've always admired suddenly become household names (stranger for them, I should imagine), especially since so many things don't make it across the pond. They absolutely could not sell John Hannah as sexy over here--just as funny sidekick. They couldn't sell Robson Green and they couldn't sell Robbie Williams. Very strange.