I've been marketing online for over 9 years and have tried many paid methods for gaining traffic, and unfortunately have yet to find the magic paid traffic fountain.
I guess that if those offering paid traffic actually had real unique visitors prepared to click on offers, then they'd surely be best to run their own CPA campaigns, and generate serious dollars themselves.
PPC - Unless you have a serious profit margin, these are even getting beyond being a viable traffic generating method.
Affilite Program - If your site is suitable get setup to run an affiliate program as this can be a great source of traffic.
Free Traffic - Optimizing your site(s) for search engines is still one of the best methods you can employ. The initial time involved in preparation can certainly payoff in the long run. Personally this & my free link exchange page is the source for most of my traffic.
David
AdSpecs Free Link Exchange
http://www.adspecs.co.nz/links/