Basically we're looking for a system that will allow pet management games. From Pokemon to Megami Tensei.
Currently I have a bastard amalgamation that combines over 100 OGL / D20 books across every genre, 3.5 D&D and all it's D20 Modern type brothers, World of Darkness (Old and New), Human Occupied Landfill, GURPS, Rifts (and Palladium in general), Shadowrun, Earthdawn, Elric!, and about another 80 books. I also have roughly another 1300 books in PDF on my external HDD.
This game is a world hopping nexus, like Sliders or Dr Who, only it uses a LOOSE D20 setup and pulls material from any idea or intellectual property in existence. I am going to finally finish the main corebook for my game but I'm weeding out how much I can put in while retaining open license.
My players have faced everything from Sunnydale Buffy and Spike, to Nazi Wookies riding Velociraptors, to Vulcan pimps and their Twi'lek hookers, to Cthulhuian demonic circuses. You name it, they can face it. And their characters are about like level 10 Mutants and Masterminds / BESM D20 style - they are sorta godlike but they fight entire empires and gods.
Either way, the game is never dissapointing and every player, even long time veterens, say it's the funnest game they've ever played.
I asked the above because I am debating what approach to take on my demon summoning section of the game - no player's offered to take that power yet.