PikiStrips is a site that has been making some waves lately in the online world. It is a site that is similar to Pixton for creating digital comics.
While PikiStrips is a nice site for what it does, I would not recommend it for education, merely due to the fact of some of the inappropriate content for schools. There is a number of clip art that a person can select and some of them just wouldn't be school appropriate such as: Borat, body parts, etc etc. However, that being said I see this as a real nice/easy site to use and can see a teacher using it to create a digital comic for their class (via a screen shot).
Give PikiStrips a try by clicking here.