Best PPC ‘referral program’?

We run a membership site with several hundred members who are always looking for ways to promote websites and get more traffic.
I do not know if Google adwords or bing search or someone else offers a referral program… I’m looking preferrably where someone get some free credits and we could earn a few bucks.
Would love to know what you all think the best program is?
-Mark

See original post by elklabone