How new is your website? I think most ad networks require proof of traffic because they have to satisfy their customers with the quality of their publishers' websites. Know what I mean?
Adsense is the most popular, I think, but I don't know if they require a more established site or not.
Why not try CPA in the beginning? I got in with Peerfly before I even had a website. I just told the guy that I was planning on using magazine and newspaper ads to drive traffic to their offers, and I was accepted. All you'd really have to do is let them know your site's topic and how it matches up with some of their offers and how you plan to start driving traffic to your site. You should be fine.
CPA is pretty cool because it usually doesn't cost your visitors any money and you can potentially earn more with less traffic than you can with PPC or PPV methods.