I'm not looking for recommendations on what music player I should use. I would simply like to know which Music players use Ubuntu's new sound menu. The only two I know of for sure are Banshee and Rhythmbox. Maybe Amarok does too? Are there any outside of these?
Players need to have MPRIS support and register themselves on the sound menu as described on the sound menu specification to place their controls in it. Currently Rhythmbox, Amarok and Banshee (via the plugin shipped in the
banshee-extension-soundmenu package in Maverick) work in Maverick, Xnoise and mpd have plugins / versions you can install externally, and work is underway to add support in Exaile and Quod Libet.
By default it's Banshee and Rhythmbox as you said but Banshee needs a plugin to work with it. I'm sure there's others that work but they might need a plugin. Amarok and Xnoise seem to work as well.