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