API for dynamic hyper-targeted ads?

Wondering if anyone knows of an API that will allow me to dynamically generate lots of ads that are targeted to specific known people (i.e., from a cookie placed on a landing page).

There are a lot of services out there for product ads. Criteo, Triggit, etc. let you upload product lists, and they'll create a large (but bounded) number of ads. I'm looking to amp it up a bit more... create ads on the fly, possibly hundreds of them per user, so that each ad may only be shown once or twice.

Anyone know of a service like this? Or a good replacement?