Delicious: Delicious makes it easy to make a collection of your favorite websites, share that collection with others, and dig into other users' collections to find more great links. Free to use.
Diigo: a great way to keep tabs on your favorite sites. Diigo allows you to bookmark a website, highlight information, place sticky notes, take screenshots, tag web pages, and more. Diigo is now compatible with Android and iOS devices as well, so you can take your bookmarks with you. Free to use.
