Jomic is a an excellent viewer for Mac comic books fans.
This open source application makes for a really handy comic book viewer. First of all, it handles of all the major image formats, including PNG and JPEG, and even supports comic book specific formats such as CBZ and CBR.
The interface is simple enough so that you make the most of your comics. You can rotate sets any which way you want and even alternate reading order from right to left, highly useful if you want to read a manga for example.
Jomic includes a useful zoom tool, with which you'll be able to zoom in on any point of a comic, and enjoy details or examine drawings more closely.
You can also extract comics which you can particularly like and save them onto your Mac, however Jomic won't tell you where it extracts to. It should normally be on the Desktop though.
Jomic is an excellent comic book viewer for Mac, which supports lots of image formats, has a good zoom tool and can rotate comics in any way.