Wade Barrett hasn't been a face yet, and I believe he could be one someday. Personally, I believe he should be a stable leader again someday (there's something about him that makes him look and sound like a leader, to me), and a face stable would be a nice way to differentiate it from his previous runs. Nonetheless, for now he stays as a heel because he seems to be more natural in this role.
I can't remember Rey Mysterio being a heel, and I couldn't imagine taking him seriously as a one. But I can hardly take him serious as a face either, so...
Cody Rhodes hasn't been a babyface, if I'm not mistaken. He could potentially make a nice turn, he's pretty good on the microphone and a nice all-around wrestler. I don't think he would have any problem getting over as an upper midcard face. But then again, he's also pretty good as a heel.
Drew McIntyre is a tricky one. His initial gimmick was a pretty decent gimmick for a heel, but he got buried so much that he might need to be completely repackaged if he's ever to seriously compete again in the future. So a future face turn might be a possibility.
Dolph Ziggler has also not been a face. I believe he's the one of this list most likely to, someday, turn. But not in a while - he's doing really fine as a heel right now, and should stay so for a few more years. I think Ziggler will be one of those guys that, once he turns face for the first time, will never turn heel again.