Joshua James at 2009-12-09 10:17:48:

Warren Beatty, actually.

Jeff at 2009-12-09 10:58:12:

100 percent agreed Joshua. Reds, Shampoo, the vastly underrated Bulworth. Brilliant stuff.

ashes1998 at 2009-12-09 11:10:19:

Steve Martin, in a very big way. I always wondered why he never took to directing his own stuff?

Burrhus at 2009-12-09 11:24:44:

Sylvester Stallone wrote himself an Academy-Award nominated script, that had an Academy-Award nominated role for him to launch his career. (Studio wanted to give it to Ryan O'Neal; then-unknown Stallone held firm.) "Rocky" is a great script and a great character which has been eclipsed by its many cheesy sequels (also, it should be noted, written by Stallone.)

Laura Reyna at 2009-12-10 18:20:11:

Jack Nicholson was a writer.

Edward Norton.

And a bunch of comedic actors... Vince Vaughn, J Favreau, Ben Stiller, etc...