One that was suggested in the DevelopingTeachers.com Teaching Tips 156 newsletter…
This Friday (23rd) is Saint George's Day and DT have a debate on that on DebateWise, as well as lesson ideas for it. Debatewise might be fun for your learners to see how many people out in cyberspace they could pull into a debate… Your first classroom debate: what kind of subject is going to interest people?!
It could also work well if you were working with another school (or another class in your own school).
The same edition of Teaching Tips also has links for Earth Day (April 22).