del.icio.us: Sort and share your favorite links, then search for content submitted by other del.icio.us users.

Digg: User-submitted, edited and moderated technology news service. Add your own stories and rate the value of pieces submitted by other readers.

Reddit: Submit and vote on stories, then receive personalized lists of pieces Reddit thinks you'll like.

Mag.nolia: Save your favorite sites as bookmarks and tag them with your own search terms for easy recall, sorting and sharing.

Newsvine: Read, write and discuss hot news stories.

Furl: Rather than just saving bookmarks to pages, Furl lets you save the entire page in a personal storage area for later retrieval and sharing. Even if the page changes, your Furled copy stays the same.

Technorati: The grandaddy of blog-specific tagging and search tools.