There is also a little airline from Crete called Skyexpress which may or may not fly to Rhodes (you can call them on 00302810223500).
But frankly I think this thread is a bit of a p!ss take. 3 airlines not enough for you on a route that's barely 150 miles as the crow flies and without any major cities involved (apart from ATH as a possible transit point)? Were you expecting some sort of underground train link between all of the 2000+ Greek islands, or do you always have to fly SQ?