How to create a wiki. This site is good to introduce students to creating their own wikispace.
Classroom Connection: Wikis could be used in the classroom from the beginning of the year and the students can each day update the class wiki so that they all know what they learned that day in case they were absent or they need to review a concept.
This is something that I would use in a fourth or fifth grade classroom. Similar to what Dan McDowell did I would create a project on Holidays around the world and have the students research each holiday and create a wiki on the holiday so at the end the entire class has access to information on the holidays of the world.
Wikitravel: I think that this is a good tool for students to use to help them explore the world without leaving the classroom.