How about Marg Helgenberger?
She played opposite Steven Seagal in one of his crap movies, but she was brilliant.
She's also very good in CSI.
Jennifer Aniston has more chops than she gets credit for. She gets noted for a lot of stuff, but she is pretty talented on screen as well.
Jack Elam, was one of the best "side-kicks" to ever show his ugly mug in a western.
Ernest Borgnine was/is also very wide ranging. From comedy, to action, to drama. He was a good good guy, and a better villan.
Jan Michael Vincent--before he fell into the bottle.