One-armed push-ups definitely work the shoulder very well. Especially if you keep your back flat and parallel to the ground(or whatever you're pushing off).
You can also do variations of push-ups, like dive-bomber push-ups and such. Get in a push-up position, but with your but way up in the air. Point your hands a little more into toward each other than usual. Lower and raise, like usual. Takes the emphasis off your chest and puts it in your shoulders pretty solidly.
The gymnastics ones like the planche work too.