ThinkFree - A website that allows you to create, edit, and publish documents that are compatible with Microsoft Office (including PowerPoint). Yeah, that’ll only save you about $300.00 or so. Free.
Pandora – Type in a song or artist you like. Pandora will start playing songs that are similar. Click a link that tells Pandora whether you like it or not. Before you know it, you’ve created a radio station specifically tailored to your taste in music. Free.
LibraryThing – An online catalogue of your personal library. Entering your books is as easy as clicking a few links. The perfect site for that obsessive/compulsive bibliophile in your life. Free.
Wikipedia – The online encyclopedia that you can write and edit. Add an article that needs to be added, or improve an article that needs improving. Very addictive. It’s like cyber-crack. Free.
Gameknot – If you want to play chess online, but don’t have huge swaths of time to spend on it, Gameknot has time controls of anywhere from 1 to 10 days per move. Find people of your own skill level (rank beginner to grandmaster), and have a blast. Even if you don’t play chess, but have kind of always wanted to (it’s okay, you can admit it), this is a great way to learn. Free.