If you're looking for a way to read comics on your Mac, Comical is a free, open source solution that does exactly that.
Despite only being only version 0.8, Comical is stable and effective. It is compatible with ZIP and RAR compressed files, and the more common CBR and CBZ comic book compressed formats. Once installed, Comical will ask to open a file, and double clicking your choice will open your comic in the resizable Comical window.
You can choose how Comical resizes your comic images as you resize the window - whether you want them to be stretched to fit, or keep their aspect ratio. You can also view in full screen, and toggle a contents panel on and off. While the contents panel is useful for finding your page, as there's no bookmark feature, reading is much more comfortable with it turned off.
There's a control bar, which allows you to rotate pages, and move between chapters and pages. This can also be reached with a right mouse click. The simplest way to flick through your comics is just using the space bar, which imitates page turning. Comical is quick to load pages and you won't notice loading at all when reading normally. The only things missing in Comical are a simple zoom feature, and a library. An iTunes style comic library would have really completed Comical.
Despite minor drawbacks, Comical is a stable, and more importantly fast comic book reader.