As 3-way, 4-way and more-way linking has grown popular, particularly with the advent and overwhelming popularity of Shawn's Digitalpoint Co-Op Advertising Tool, other systems have popped up to attempt to create similiar forms of link sharing/trading.

At SES NYC, Alan Webb - Webby from SEOChat - informed me of a new, free link network system that he had helped to develop. The tool, Link-Vault, allows you to submit links for the network to include and serve links on your own sites, similiar to the Co-op network. The best part about the site is explained on the homepage:

Each website added to the network will be vetted by a person before any links are placed to ensure it meets our strict quality guidelines. Should you wish to use your Vaultage quota to provide text link adverts to a website not in the system, then this website will also need to pass the vetting.

I'm looking around for a site to test this on, but forum feedback has been positive in general - see Sitepoint & SEOGuy.