Let's all collaborate

E2BN has excellent collaborative tools- http://www.e2bn.org/. Discovery box and Museum box are also very good presentation tools-good for all those fed up with  PowerPoint!
Creaza has a whole suite of possibilities: http://www.creaza.com/
and don't forget mind mapping collaboration with Mindmeister.
Google Apps for collaboration will desrve a post all of its own at a later date!

An oldie but goodie- children collaboratively annotate photos/pictures or videos
http://voicethread.com/#home
Share your favourite parts of the day
http://www.memiary.com/
Great slideshare with ideas for Memiary
http://www.slideshare.net/markwarner/using-memiary-in-the-classroom
Ether pad
Real time sharing by multiple users
http://etherpad.com/