I've run across several websites recently that I find to be very useful/interesting. Don't click on them now, necessarily; bookmark them and use them when you need some knowledge.
Yahooligans Reference. Okay, it's for kids, but it's a great source for looking up information. The Spanish dictionary there is the best I've found online (and I've looked quite a bit). Other cool features include Shakespeare's works, Quotations, a dictionary and thesaurus, and a World Factbook.
Your Gross & Cool Body. Also for kids. Ostensibly. So what?
Hmmm, come to mention it, National Geographic Xpeditions is for the younger set, too. If I were a teacher, I'd use the lesson plans available there. I'm not, so I probably won't. The Atlas, though, is a great source of maps. Definitely bookmark-worthy.
Also of interest, but not of the abiding kind: China is trying to fix some of its Engrish problems.
Finally, Yahoo and Forbes are teaming up to deliver an Email Time Capsule to you in 20 years. I wonder if they've had many takers.