Some sites I'm looking at to see how they might work in classrooms:
Pearl Trees   --  http://www.pearltrees.com - digital portfolios online?
TitanPad - http://titanpad.com/ - take group notes with no signup
Tagxedo -- http://www.tagxedo.com/  - upscale Wordle that I haven't looked at lately - free.
Sticxy - http://www.stixy.com/ - online bulletin board.
Pinterest - really???

More image editors
Besides Sumopaint:

http://pixlr.com/ - can be downloaded (Windows) or can work online with no signup.
http://www.picmonkey.com/