Diigo is a social bookmarking/research tool that is very similar to del.icio.us but in my opinion has the edge in terms of features, usability and aesthetics. They have just released version 2 of their look and feel and it is really nice. One of the best enhancements is in the Diigolet bookmarklet, one of the tools you can use to bookmark and forward sites to others. Unlike most bookmarklets which are fairly plain the Diigolet actually looks and functions almost as good as the dedicated Firefox extension whilst at the same time working on a range of different Internet browsers. Checkout the video below to see what I mean...
If you have not tried any social bookmarking sites or feel like you could use a change I'd recommend giving Diigo a try. Joining up is easy and they have some nice importing tools for getting all your old bookmarks out of your browser or competing bookmarking service and into theirs.