Delicious

Delicious (formerly del.icio.us) is a social bookmarking web service for storing, sharing, and discovering web bookmarks.
Delicious uses a non-hierarchical classification system in which users can tag each of their bookmarks with freely chosen index terms (generating a kind of folksonomy). A combined view of everyone's bookmarks with a given tag is available; for instance, the URL http://delicious.com/tag/wiki displays all of the most recent links tagged "wiki". Its collective nature makes it possible to view bookmarks added by other users.