My favorite e-book app is the free Stanza. Text on Stanza just looks nice -- it's well formatted and designed for easy reading, with wide margins and spacing between lines, and a big selection of fonts. You can choose from about a dozen different text styles or customize your own fonts, colors, line spacing and other features.
You can buy e-books from within the application; the app accesses books from the Fictionwise bookstore and other sources of paid and free books. Although Stanza developer Lexcycle is owned by Amazon.com, the app can't read books formatted for Amazon's Kindle e-reader. For those you'll need the Kindle app, discussed below.
Stanza integrates with the iPad Web browser, so if you find an e-book on the Web in any of a variety of supported formats, including ePub and eReader, you can download the book in your iPad browser and the iPad will ask you whether you want to save the file to Stanza.
Alternately, the free Calibre software for the Mac, Windows and Linux lets you convert documents from a range of formats including RTF, PDF, HTML and ODT to e-book formats. Calibre manages your e-book collection and transfers e-books from your desktop to the iPad and a variety of other devices.
E-books: More good options
The two most popular e-book apps for the iPad are Apple's own iBooks app and bookstore, as well as Amazon's Kindle app and store. Though I prefer Stanza, they're both fine e-book readers, and they're free.
The iBooks app can be a little annoying. When you open a book in iBooks, you see a brown border around the page that's supposed to resemble the cover of an open book. And when you turn a page, you see a page-turning animation. These features make the app a great demo, but they're just distracting when you're trying to sit and read.
Also, the selection of books in the iBooks store is somewhat scant. Often, I don't find what I'm looking for there.
Another issue with the iBooks app: It's available only for the iPad and for iPhones running iOS 4. That means the books you buy from the iBooks store are locked to the iOS platform. Amazon's and Barnes & Noble's apps, discussed below, are available for multiple platforms, and, while Stanza is iOS-only, the stores that sell e-books for Stanza are cross-platform.
Amazon's Kindle app for the iPad offers a far better selection, and a better reading experience too. There's less clutter, and the annoying page-turning animation is optional; you can set it so that pages seem to just slide quickly. (The Barnes & Noble app offers the same sliding action; with Stanza, you get your choice of an iBooks-like page flip, a slide effect or no page-turning effect at all.)
Amazon recently upgraded the Kindle app to include support for embedded video and audio clips, and it released books supporting the technology, including a travel book, Rick Steves' London, and Together We Cannot Fail by Terry Golway, a history book about Franklin D. Roosevelt. Right now, there are only a few titles available with audio or video, but it's a technology to watch; I expect that we'll see embedded audio and video becoming standard soon. Nonfiction books will use audio and video to supplement the text, just as photos are now used, and novels could benefit from interviews with the author or animations depicting key sequences in the story.
The free BN eReader for iPad, from Barnes & Noble, is a promising up-and-comer, offering a good selection of books and a nice user experience, including the usual array of font and color choices.
While I'm talking about reading on the iPad, I don't want to forget the Mobile Safari browser that's built into the device. The plain old browser is a great tool for reading. When you come to a column of text (like an article in Computerworld), tap twice on the text and the browser zooms until the text fills the width of the screen, as shown below.
And here's a tip for reading e-books in bed: With the screen lock switched on, the text you're reading won't rotate if you read while lying on your side. The screen lock button is located on the right side of the device.