Using Pay-Per-Click (PPC) Search engines you only pay when
someone visits your site rather then how many times your ad or link is
shown.
If you are not already with the PPC concept visit: http://www.adbility.com/WPAG/ba_click.htm It also will share with you the pros & cons of many of the more popular sites.
The key ingredient to selling is traffic. If people don't visit your site, you won't make any sales. Below is a great collection of pay-per-click resources to help you drive targeted traffic to your site.
http://www.sprinks.com
http://www.overture.com/
http://www.findwhat.com/
http://www.ah-ha.com/
http://www.kanoodle.com
http://www.searchhound.com/
http://www.powerclick.com/
http://www.zeedee.com/
http://www.google.com/
http://www.searchgalore.com/
http://www.webranking.com/pay_per_click.htm
http://www.7search.com/
http://www.hitsgalore.com/
http://home.pennyweb.com/
http://www.Aaddzz.com/
http://www.NetFlip.com
http://www.onesearch.com/
http://www.valueclick.com/
http://www.i-clicks.net/
http://www.win4win.com
http://www.WebsiteSponsors.com/
http://www.click2net.com/
http://www.mamma.com/
