PPC engines can be categorized into two major categories "Keyword" or sponsored match and "Content Match". Sponsored match displays your listing on the search engine itself whereas content match features ads on publisher sites and in newsletters and emails.
If you got a personal blog or site you can use adbrite and bidvertiser as they have low payout of $10. I use adbrite and i am really happy the bids per click i get. Try it.
