Comic Life is one of my favorite comic generators. Comic life comes as a nice little perk on Apple computers, but for a price you can also install Comic Life on Windows. If you are looking to add comics to your iPhone or iPod Touch, Plasq.com has unveiled Comic Touch.
There are many comic creators available online. My favorite is Pixton. A general account with Pixton is free. Pixton does offer an education version (Pixton for Schools) starting at $1.00 per machine.
Elementary teachers might want to use an application that is not tied to a social network and that does not require students to sign into a website. Therefore, you might take a look at ReadWriteThink's Comic Creator or Make Beliefs Comixs. Both Makebeliefcomixs and ReadWriteThink offer the option to print a completed comic, however a save feature is not present.
To see a list of other online comic creators and ideas for integration take a look at resources that Tuanua Swartz and I have put together on wikispaces or blogger.
Let me know if you have a comic lesson plan or an application that works well for your classroom, I would be happy to have you share.