Books.app is a simple eBook reader for the iPhone. It reads HTML and text files stored in your Media/EBooks folder, and is smart enough to enter subdirectories, if, for instance, you’ve broken a book down by chapters.

Changes:

Preferences pane! Choose your font, font size, navigation bar auto-hide preference, and much more!
Chapter navigation buttons on the bottom toolbar, at long last! Go forward and back without returning to the browser view.
Human-friendly browser sorting! You can use Chapter 1, Chapter 2… instead of Chapter 001, Chapter 002…

http://code.google.com/p/iphoneebooks/