Blogging With Students:
Kidblog.org - If you're just getting started with blogging with your students, this is a great place to start. It's currently free, easy to set up, and doesn't require student email addresses.
WIkis
PBWorks - Easy, free-to-use wiki provider. (That's what this wiki is...)
Wikispaces - Free for education use. Also very popular.
Educational Resources - Free Resources for teachers