Delicious

It 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).
Delicious has a "hotlist" on its home page and "popular" and "recent" pages, which help to make the website a conveyor of Internet memes and trends.