There are many online sites where students can easily make their own comic strips. Most of the ones I’ve linked to my site, but not necessarily all, then allow them to email the url’s to their teacher to post on a website. I have several listed under Student Comic Strips on the Examples of Student Work page on my website.
I’ve just put a link to a brand new site called ToonDoo, which looks like it might be the best of the lot. I heard about it from a variety of places, including the Langwitches blog. It’s the last link listed in that section.