Here’s a cool site that is sort of a primer on Comic Book Grammar. Very creative and graphic ways to express emotion and forms of speech. POW!
After visiting this site I realized that there are a lot of online comic book tools, here are a few:
2. Cool Text Graphics Generator at http://cooltext.com/Logo-Design-Comic is meant to help design a business logo, but the Comic option is great for creating the “sound effects” graphic punctuation seen below in the “BAM!” graphic. (I added the yellow star for emphasis.)