Wikipedia
I thought I'd just mention that over the last few weeks I've become hopelessly addicted to Wikipedia. It's an online encyclopedia that can be editted by anyone. It's wonderful. I can go there for hours and just browse random pages, soaking up new information about practically anything. For an encyclopedia that can be vandalized by any yahoo who surfs by, it works amazingly well. It's also a great exercise in writing; if I find an article that needs work, I can help fix it. It gives me a sense of accomplisment to contribute to something larger than I am.