The list is enormous to be honest. The most common seem to be (that I've heard of anyway) Sambo, ROSS, Kadochnikov Systema, Sokoli Stalina and Rukopashnii Boi. Then there are regional and/or family styles of work. I wish I could give more of an answer for you.
Are Sambo and ROSS considered susbstyles of Systema? The former especially I thought was a different RMA. Perhaps as you said in another post "Systema" is so generic that all forms of RMA would fall under that heading. I was really thinking more in line of the Systema associated with the Spetsnatz.
oooh...I gotcha. The Systema used by Spets goes by a couple of different names. To the Spetsnaz, it's referred to as Combat Sambo Spetsnaz. Rukopashnii Boi is another name used, though it's the same as the Sokoli Stalina.