New Ajax social bookmark URL(you can see with what tags one have bookmarked you) and tag search. Says it will be adding more social bookmarking query services almost daily.
TagCloud is an automated Folksonomy tool. Essentially, TagCloud searches any number of RSS feeds you specify, extracts keywords from the content and lists them according to prevalence within the RSS feeds.
B. Krause, R. Jäschke, A. Hotho, and G. Stumme. HT '08: Proceedings of the Nineteenth ACM Conference on Hypertext and Hypermedia, page 157-166. New York, NY, USA, ACM, (2008)