PPC - Get More Visitors To Your Website

PPC ads appear like search engine listings but are actually paid advertisements.  The highest bidder gets the highest position. 
Overture.com, Espotting.com and FindWhat.com are all examples of PPC engines that you can join.  The advantages are that you can get a Number 1 listing almost immediately, the disadvantage is that you have to pay for every click through.

Google AdWords is not strictly a PPC Engine but it is usually lumped in with the others as you still have to pay for each click you receive.

You can find loads of different Pay Per Click search engines here - http://www.payperclicksearchengines.com - infact, there's hundreds!!