Regular readers of this website will no that I have a real passion for the use of comics and graphic novels in the classroom. My favorite free on-line comic creation tools at the moment are Comic Brush and Pixton.
Comic Brush (www.comicbrush.com) is a bit like a free version of Comic Life and it allows you to make on-line comics for the iPhone / iPod, comic strips and full length comics. It is easy to use and you can either insert your own pictures into the comic strip or download an art pack (small charge) or do a bit of both. The art packs are great as they allow you to introduce licensed characters / artwork such Judge Dread or manga into your comics.
(click on the image to make it bigger)
The problem is despite these tools being free they may be blocked by some local education authorities and they rely on a reasonable bandwidth in order for them to work properly.
As a result I like to remind teachers that you can actually produce fairly good comics in PowerPoint. I recently produced an Innovative Teacher InnoVid on the subject which some people may find interesting (version embeded below).
You can find out more information about InnoVids here.
And if thats not enough comic stuff for you you could also have a look at these 100 tips, tools and resources for teachers.