Wolfram Alpha is an interesting web 3.0 search engine. It can convert currency, provide statistics, recall historical information and provide quick answers to quirky questions on the fly. It also generates an easily downloadable PDF that contains the information retrieved for a particular search. This is a great tool for research or for illustrating complex concepts in the classroom.
OK, I know this sounds like cheerleading, but you just have to play with it to see how much fun it can be. Type in a term in the search box below or visit the examples page to see how robust this tool can be for the classroom.