Celeb sites, proxies, games, warez and similar sites get really good traffic and since traditional PPC/CPM don’t pay well, you can buy banner space for like $20/month on them and get easily 1000’s of visitors.

But Make sure your site appeals to the crowd. I mean showing “Mortgage calculator” or “debt relief” links won’t work on a Manga site but a “Gadget” site or a “sports car” site will surely work on it.

Many webmaster (almost all nowdays) have “Buy traffic” section where people sell traffic from there site. You should be get way way cheap deals there instead of going through any CPM networks.

Tip – Always buy banner ads from such sites and make sure you nofollow the link from the site. If the Ad gets shown on 20k pages, than you certainly don’t want link from 20k pages of same site.