The Digital Comic Museum is a crowd-sourced collection of hundreds of classic comic books that are now in the public domain. Register users can download these comics from the site. You can browse the galleries to find comics to download. If know the name of a comic or comic publisher you can search for it by name.
Applications for Education
I learned about The Digital Comic Museum a week in a post by Alan Levine. Alan mentioned it in the context of using The Digital Comic Museum as a place to find comic artwork to remix magazine covers. Taking the idea another step I might have students create posters or news magazine covers about historical events, about key elements in a fiction work they're reading, or use the artwork in political cartoons they create.