Writecomics.com is a really simple comic strip generator. It does not require a registration to start creating. It is free and really easy to use with your students. There is a variety of characters and backgrounds to use. This tool is also perfect if you want to include some humour in your classroom as it has a section with alien characters. After creating your comic the website gives you a link to your comic strip and you can grab the picture online or you can save the comic as jpg file to your computer.
If you click on the image below you can see a tutorial-like video:
More comic-maker applications described in this blog: