I had the same problem a few weeks ago when I was looking to make my routine a bit more well rounded.
At the moment I am doing:
Pike Press, depending on how you do them, they may have more focus on your chest than on your back. Compare them with Pike Push Ups. The closer your feet are to your hands the more focus you get on your shoulders, so both exercises are often mixed up or simply just called Pike Push Ups. (as in the videos below)
Side Bridges and Bridges are mainly focused on the abs and the core in general but use a lot of shoulder muscles for control.
When I look for new exercises I often check out Youtube and search for the muscle group I want to train and checkout the exercises on other sites (like exrx) afterwards.
Some videos I recently bookmarked:
Best Bodyweight Shoulder Exercise - shows that you can do pike push ups even with a cat in the way.
4 Killer Shoulder Exercises *Home Workout Routine* - silly music, but good explanations.
10 Shoulders Exercises (body weight) - just some dude doing exercises, no further explanation given.
Be careful with videos though, you never know if they are done with good form, so check at least two or three other resources before attempting an exercise. As always: if it hurts or feels strange, don't do it.