Ask HN: Advice on finding big brands to advertise on my site.

I have a facebook app which is getting some serious traffic (2m+ visitors a day). It should easily be enough for a big-brand ad deal, but I have no idea where to start. Are their 3rd party companies which act as the middle man and help negotiate ad deals like this for a cut? Is hiring a full time ad sales person the way to go? Do companies like Coke expect a rich presentation selling them on the merits of advertising on your site, or is a short email and traffic stats enough to get their attention?

Sorry, not going to post the link. In this instance it's the idea (and it's easily reproducible), not the execution..