When I'm bored I surf the Internet, do homework or read books. Or I go to digg.com or use Stumbleupon. There's a cool little browser plug-in for Stumbleupon that lets you check out random sites that other people think are interesting (http://www.stumbleupon.com/). Basically how it works is that you fill in some categories of things you find interesting and then you can choose to see an interesting site, image, video, news item, whatever, that other people have flagged as interesting (or Digged, to use digg.com's terminology). It gives you results based on your chosen categories. I have found so many cool things on the Internet that I wouldn't have found if I hadn't known about Stumbleupon.
But a little word of caution: it can waste a lot of time. If you're bored, it will provide you with interesting information and entertainment, but only use it if you're desperate as it can waste lot of time.