Also note that now also Tome of Magic is allowed, and honestly said love it! It haves very intresting spellcasters or rather say users of magic (spellcaster is unfit term becuase none of them use spells expect one but in end spells transform into supernaturall abilities). Anycase one of our players seemed to be intrested to be summoner, well, there is PrC called 'Fiendbinder' who must know Summon IV spell and Truespeak (a new skill) 10 ranks but in end you can bind demons or devils under your will via ceremonies and best of all; The demons and devils stay whit you 24 hours 7 days of the week (henceworth permamently until dismissed) but bad side is that the fiend in question msut stay 10'ft of you nor cannot go farther than 1 mile until it get risks to get loose plus none of the fiends will be your friends. In end of 10lvl PrC you get +7 to any sepllcaster class (which gived the needed summoning spell) and also can get Baatezy or Tanari template for short while or be able summon 1d6 lesser demons/devils or 1d4 greater demons/devils once per day plus you are able to summon whit swift action a extra demon/devil fight for you for 1 min per level.
Also the cheesiest part; There is NO LIMIT how many demons or devils you bind to yourself but demons and devils, altough they do not harm you, they MAY harm anyone else who come 10'ft of you!