
Dragonchess Player |

You could probably adapt the thaumaturgist PrC from the DMG with only a little effort.
Some other possible (non-OGL) starting points: acolyte of the skin (CAr), diabolist, demonologist (switching alignment/outsiders summoned), and disciple of Asmodeus (BoVD).

Zohar |

I have a concept for a high level Devil Binder. Something that not most of them would do or be able to accomplish.
But basically a Wizard who has fused his soul with the essence of an Ice Devil. The Ice devil is bound to him and can manifest partially as a sort of aura around the Wizard, granting him the use of a few of his spell-like abilities, and his fear aura.
Working on some fan-art type stuff for it too. I just found the whole idea of Chelaxian Devil Binders (And the other variants of Wizards with different kinds of familiars) very interesting. So I decided to expand a bit on this particular Devil Binder.

F33b |

I see the Fiendbinder has already been suggested. It should be relatively easy to adapt that PrC to a campaign that doesn't use Truenaming by just using Diplomacy checks for Devils (after all, they are lawful beings) and Intimidate/Bluff checks for demons. It may be necessary to tweak the DCs upwards a bit, but the overall effect should work well.