Thinkature - A visual collaboration tool.
Wallwisher - Works like a notice board. Add, drag and move post-its. Great for brainstorms.
Corkboard - online bulletin/notice boards
Stixy - online bulletin/notice boards
Webklipper - Allows you to annotate any page with a highlighter and/or post-it style notes.
VoiceThread - A collaborative, multimedia slide show that holds images, documents and videos.
Primary Wall - A web based sticky note tool designed for schools.