Deeee.licio.us!

Del.icio.us is probably one of the best tools ever designed for the web.
What's del.icio.us? It's a social bookmarks manager. It lets you post sites to a personal bookmarks collection that you can access anywhere! You can assign tags to all the sites you post,which lets you organise your bookmarks around these tags. For example, right now, I've got 320 bookmarks with the tag "games," and 204 with the tag "comics." You can assign as many tags as you want to a bookmark. So if you find a blog about comics and games, you can assign both tags to that bookmark.
The tags feature together with a built-in search function makes it an extremely useful tool for organising a bookmarks collection, especially if you have a huge one like mine (914 sites at last count and growing daily).
Since del.icio.us is a social tool, anyone can view anyone else's bookmarks as long as they know their username on del.icio.us. Here's mine: del.icio.us/hazylium
Take a look around. If you feel confused, go to the about page. It'll tell you all the basics and get you up to speed. Alternatively, here's a great beginner's guide.
The most interesting feature of del.icio.us, to me, is it's popular page. This page keeps track of, you guessed it, the most popular pages bookmarked on del.icio.us. It's really interesting to see what kind of pages come up. It's kind of like a radar for tracking what's new and hip on the web.
I'll post more info about this really cool site later. For now, I'll point you towards an excellent blog post about del.icio.us tools that's regularly updated with new info: Absolutely Del.icio.us - Complete Tool Collection- I got the link for the beginner's guide from there too.