Websites to use for posting artwork, commenting, exchange ideas on each other's work. Other documents can be added

www.stixy.com can post artwork, write comments, give feedback

www.carbonmade.com is an online art portfolio.

www.voicethread.com can also be used for peer assessment, leave audio comments and write comments

www.twiddla.com whiteboard concept of having real-time conversations, lectures, save images of artwork. You are able to invite students to join you on this lecture and add comments.

Basically there are lots of tools that have similar functions. It's all about how you want to manage, collaborate and communicate with your students.