I would have killed for something like this when I was a kid. Well, okay, I would've killed for the Internet when I was a kid. But I saw that Marvel has a little create your own comic app on the Marvel Super Hero Squad site.
It's a pretty simple drag-and-drop design, and you can scale the graphics and word balloons. You even get a choice of cool comic fonts to use as well.
If you don't feel like you have an epic comic book story to tell, you can start with a single comic strip. I gave that a shot, and I was surprised how quickly you can put something together. Click to embiggen.
Yeah, I think we can see why I don't work for Marvel...