Thanks to Pete the Fireman for sending this along:
This video, aimed mainly at cyclists, shows some basic tube-and-partner exercises you can do to strengthen your shoulders.
Another group commonly internally rotated and round-shouldered consists of anyone working mainly on a computer. You sit leaning forward towards the monitor and shoulders rounded and forward in order to best type on the keyboard.
While the video above isn't really a true substitute for a proper, integrated workout that puts emphasis on shoulder health and pull motions, nevermind adjusting your work environment to get rid of that internal rotation in the first place, it's very good stuff.