I made a website that has pictures of every astromech that appears in the movies that you haven't yet made. Many of these are extremely obscure, and you can't easily find their images published anywhere else if at all. If you can take the time to look through the different pages, I am certain that you will find a number of cool droids that would make excellent figures. http://www.angelfire.com/droid/astromechs/
PS - I am adding new droids to the site all the time. In particular, I have good shots of two never before seen droids that were used in X-Wings and Y-Wings coming by this summer!