Alright chumps, here's the skinny. You download a comic book reader - the Cdisplayex one linked above is free, but use whatever you'd like - something that reads .cbr files is most useful. Then you head on over to Anna's Comic Cantina here and set your search like so:
...and you've got access to 2mil free comics, give or take a thousand or so.
Here's what Cdisplayex has to say about itself:
Free, Light, Efficient CBR Reader. It is the most popular comic book reader. It is able to read all comic book formats (.cbr file, .cbz, .pdf, etc..) and Manga. Everything is designed to give you the best reading experience, it load comic books immediately, reading is fluid and comfortable.