Best PPC for advertising in the US?

Hi,
First time poster here, writing from Little Old England. I’m looking to advertise via PPC in the US for an affiliate project: aside from the big three (Google, Yahoo and MSN) are there any other big PPC networks that are particularly effective for the US market? And any that are specifically good for local/geo targeted search?
Apologies if this has been asked before, I’ve had a dig around but couldn’t find an answer to this specific quesiton. Thanks!

See original post by zentimo