You can chuck that Merriam-Webster dictionary that's sitting on your desk out the window (along with all your magazines). It's been iPad-ised and it looks beautiful. Also, it's free.
Hold your iPad in portrait orientation, and it's kind of a ho-hum app that lets you search for words. Turn it landscape, however, and it acquires a scrollbar that lets you smoothly browse through every word of the dictionary. Tap to get your definition. It's not quite an ebook, but I like it better than other apps, which just feel like touch-friendly websites. [iTunes]