eManga

eManga is a free application for Windows, Mac OS X and the iPhone™, iPod touch®, & iPad.

It works as both a manga-viewer and a library organizer all-in-one. And there's the Mangacast system to allow you get get Manga releases in lighting-speed.
The eManga reader lets you read your manga right from your library. OpenGL acceleration uses your graphics card for rapid page viewing and allows you to instantly zoom or fit the page to your screen. You define your own custom keyboard and mouse controls. The overhead display gives your information about the chapter you're viewing, and can be turned on and off with the click of your mouse.
eManga introduces a new concept to the world of manga: the Mangacast. Mangacasts are feeds of manga chapter releases. When you subscribe to a mangacast, eManga will periodically check it for updates, and optionally download new releases for you. No more constantly looking around for new releases - now the new releases come to you!