Just sat down to try to compile the stuff that exists about summoned monsters. Haven't included the stuff for specific gods and the like, just Core Rulebook and Champions of Purity, among other things trying to find what, if any, languages you need as a monster summoning class. The results are:
Abyssal Babau, Bebelith, Dretch, Glabrezu, Hezrou, Nalfeshnee
Auran Air elementals
Aquan Water elementals
Celestial Babau, Glabrezu, Hezrou, Nalfeshnee
Draconic Babau, Glabrezu, Hezrou, Nalfeshnee, Pseudodragon
Ignan Fire elementals
Infernal Hell hound
Sylvan Blink dog
Terran Earth elementals
Soooo... if you get Draconic, you get all the bigtime demons and the pseudodragon. Add Abyssal for the bebelith and dretch, then choose if you want to give specific orders to what kind of elementals, and whether you care about summoning dogs. Also note that the demons and the pseudodragon have telepathy, but the rules do not say if you can start telepathic conversations with creatures who have telepathy, so it may not be useful for giving orders.
Thoughts?
Actually, the only reason you need celestial is to talk to a few demons, and then there are strictly better alternatives in Abyssal and Draconic. The list above were the only ones that did not have Common and/or Truespeak/tongues always active. Infernal is only needed for hell hounds, and Sylvan is only needed for blink dogs.