ZoomTags is an API-based solution and allows blogs and other websites to place a commercial tagcloud on their sites. Like 1000Tags, Zoomtags allows advertisers to bid on tags or keywords in a tag cloud. When someone clicks on a tag, they see a set of advertiser results. This are Adsense type ads in a tagcloud.
Website owners will have a variety of tagclouds to choose from.
ZoomTags, which is part of ZoomGroups, already has a fairly established advertiser network that has been in place since 1999.
Nothing, of course, stops Yahoo and Google from implementing a similar interface if this proves to be a better way for some sites to serve ads.