How about Cameron Crowe? I thought he brought an amazing amount of heft and gravity to his performance in Minority Report
I always liked Roman Polanski's acting in Chinatown. I thought he was at once hilarious and frightening. He has a lot more acting credits that I ever thought he would.
Mathieu Kassovitz was great in Amelie, among others, and The Crimson Rivers is one of the great action movies of the last five years
I thought Lawrence Kasden was hilarious in As Good as it Gets
Vin Diesel also started out as a director, just before he got a little too involved with the whole "diesel" lifestyle
James Toback is a serviceable actor, for the most part.
I think Richard Linklater has a natural nack for acting, although he tends to get a little marble mouthed sometimes.
Jim Jarmusch is great, acting and directing
All I can think of now.....