I particularly enjoyed his roles in Ghost Rider and Face/Off. Even though I think it's a universally hated movie (Ghost Rider). I enjoyed Lord of War, I think it's high time that I go back and watch that one... I wonder if it's on Netflix...
Lord of War is probably his best film. At least in the serious vein. I think a large part of this stems from his not acting like Nicholas Cage. The Rock is his best non-serious role. Still decent acting without any of the insane craziness he is known for now.
The Rock really has to be Michael Bay's best work. It has the perfect blend of action and plot. The action isn't so over the top and mind numbing, the way Bay got with his later films. He managed to achieve and optimum blend of serious and silly with a fantastic cast. Sean Connery plays his role brilliantly and his constant jabs at Cage's whining always make me laugh. "Your besht? Your besht!? Looshers alwaysh talk about their besht!"