Planar Binding and Planar Ally both, according to the spell description in the PHB require a deal to be made with the creature that is summoned. Planar Ally, however, is the more diplomatic and less demanding of the two (since it is a request of one's deity to send the creature), but it's also less flexible (one can only summon the planar ally of the deity in question, which is preset). Planar Binding involves yanking an outsider or elemental creature from where it is on the planes forcefully and trying to cow the thing into obeying in exchange for what is offered. Overall, Planar Ally is probably more of what you're looking to use, Edd.