First there's 
Skrbl, the online whiteboard that allows mutiple users. Then there's 
Sketchcast. It allows you to create an animated drawing while recording your voice so you can create a drawing with explanation. I also like the potential for 
Bubbl.us which allows easy creation of graphic organizers. Online picture storage is also key so I like to use 
Picasa since I'm a googlehead. A great place to host podcasts for free is 
PodBean. Then there's the place to put it all. I have been playing around with the 
edu2.0 site and it seems to be pretty easy to navigate. I also have an account at 
Wikispaces which has free stuff for k-12 educators.