AdSwappers
Manual Surf, 5:4 ratio. 20 second timer. Also offers a variety of free advertising including clickthrough, downloadable and search exchange.
Share-Traffic.com
A trading clicks site that offers a 2:1 ratio. Also paid service for 1:1 ratio.
TextTraffic.com
Members place six links on their site. Each time a new member joins from the members site, their ad goes on the new members site for six levels.
VirtualTrafficJam
Each time a member opens their browser they see another member's website and earn hits to their own website at a rate of 1 visitor for every 2 sites visited.
WebBizInsider.com
Traffic exchange which allows you to get traffic viewing other members sites. Also has other free tools to help promote.