3. Diigo - A really fantastic social bookmarking and annotation tool. Like del.icio.us, Diigo arms you with web browser toolbar that lets you publicly share and organize your website bookmarks. However, Diigo expands upon this premise by allowing users to highlight, clip, and make sticky-notes on the websites you bookmark- and this makes it a powerful research tool (especially if you're me- prone to bookmarking websites that mention anything having to do with my thesis, and forgetting why they were important later).