fixya - is a great tool that can help you fix and troubleshoot things. There is tech support and manuals at your fingertips. I'm not sure if it would really come in handy for your classroom, other than to fix things around the room without having to call tech support :) But it is a super cool tool!
lulu - is a cool tool that allows you to upload your documents and publish them. This could be a cool idea to write a book as a class and have it published. It does cost and I found it a bit confusing to know what the exact cost to write a book would be. However I did find quite a lot of great teacher resources available for purchase, and you have the option to download or purchase a hard copy.
live mocha - is a wonderful language tool. Teachers can brush up on their 2nd language or they can prepare for their extra certifications! The best part it's free!! You can enroll in free classes, chat with others, and so much more. They even have flash cards to help with your language journey. I know I will be adding this site to my del.icio.us bookmarks! What a great tool. Teachers can also use this to aid students in learning a new language.