Sequential started life as an image browser, and it's still a nice way to view batches of images, but it's also turned into the best Mac comics reader out there. I've tried other apps like Jomic and Comical, and found that they don't measure up to sequential in terms of speed, stability, and Mac-like feel. For whatever reason, large .cbr and .cbz files tend to crash most Mac readers. Not Sequential, though. It handled a 400-page collection of files without even a beachball.
On top of being fast and crash-free, Sequential is also just plain pretty. It displays EXIF data for photos in nice, Leopard-style bezels, and has all the resizing options you could want for either photos or comics pages. Navigating entire folders is no problem, and there are even next folder / previous folder controls. There's also a slideshow mode, which might not be that useful for reading the latest manga, but comes in handy for batches of photos. Bottom line: if you read comics digitally, Sequential is well worth the download.