Books Optimized for Mobile Devices
Google Books and Project Gutenberg both make books available for use on mobile devices. These are excellent resources for accessing classic literature and other public domain books.
Google has created a Google Books web site optimized for use with mobile devices. To use it simply visit http://books.google.com/m using Safari.
Normally Google Books contains scanned images of actual books. This was useful, but made the books harder to read on mobile devices with small screens.
This new mobile service instead uses Optical Character Recognition to scan the text off the pages. It then displays this as text in your Safari browser, allowing the text to wrap within the browser. This makes it much easier to read. However, there may be errors introduced by the OCR process.
One problem with Google Books Mobile is you need to have internet access to use it because it relies on Safari.
For more information see the Google Press Release called "Google brings e-books to mobiles".
Project Gutenberg has been around for many years. All its books are available in text format, and many in HTML, suitable for reading in Safari. Many books are also available as audiobooks. The mp3 files can be downloaded and played on your iPhone or Touch.
A search for "Gutenberg" in the application store will find many applications that can read Project Gutenberg books off-line. "Stanza" is an excellent free off-line book reader that accesses Project Gutenberg (and other) books.