Comic Book Archive files -- they have .cbr and .cbz extensions -- are really just compressed folders of .jpegs. Extract the files into your folder of choice using BetterZip (or any other extracting utility). Open the folder in the Finder. Select all of the files and hit the Space Bar.
Click the full screen button in Quick Look and press Pause; that way it won't move to the next page before you're done reading. Use the left and right arrow keys to navigate through the book. Voila, your own comic book reader, and zero resources used.
[robg adds: I added the Wikipedia link, as I wasn't familiar with .cbr and .cbz files. I'm not sure if all extractors will understand those filename extensions, but if not, you might be able to just change the extension to .zip or .rar, etc. and try again.]

