After joining the Yahoo group, http://groups.yahoo.com/group/eiditarod/ , our grade is following the race. In our class, we are having a boys v. girls competition. The Yahoo group provides guidance and forms for each step of the race. Students are blogging about the progress.

lino is an online web sticky note service that can be used to post memos, to-do lists, ideas, and photos anywhere on an online web canvas. Here's a link that describes 50 ways to use it in a classroom http://21centuryedtech.wordpress.com/2011/08/14/part-1-digital-collaboration-series-linoit-no-student-log-in-plus-50-integration-ideas/

Kidblog is built by teachers, for teachers, so students can get the most out of the blogging process. Kidblog meets the need for a safe and simple blogging platform suitable for elementary and middle school students. Most importantly, Kidblog allows teachers to monitor and control all publishing activity within the classroom blogging community.

Curriki, the online education community, is building the first website to offer free, open-source instructional materials for K-12. We have thousands of free worksheets, lesson plans, exams, project ideas and activities for English language arts, math, science, social studies, technology integration and other subjects.

Global SchoolNet's uses content driven collaboration. The age ranges vary and you are able to set the filter for your class level. I like this because it provides options to choose from, so you can pick based on the interest level of your kiddos, as well as the topics you are teaching. The only pitfall I could see would be if there was nothing relevant.