iPhoto ($5 in the App Store) is an app designed to let you perform a wide variety of tasks, including organizing photos, creating slideshows, creating Web-friendly scrapbooks, and editing, cropping, tweaking, filtering, and retouching photos.
Once you start relying on Instapaper ($4 in the App Store), you'll wonder what took you so long. The idea is simple: Reading on your iPad is much more pleasant than reading on your Mac's screen. When you come across lengthier articles online, you tap the Instapaper button, whether in your browser, RSS reader, or Twitter client, or in one of the many other apps that integrate with the Instapaper service. The next time you launch Instapaper on your iPad, it will pull down the text of that article, as well as any inline images--but it will leave all the navigation, social networking modules, and Flash advertisements by the wayside. You're left with just text and images, and you control the font and brightness and all that other good stuff. The app also makes it easy to discover more good Web content to read, based on your friends' suggestions.
Tweetbot ($3 in the App Store) began life as an excellent Twitter client for the iPhone, and the iPad version is even better. The app's unique interface and brilliantly implemented gesture support make it not only a powerful app for reading and posting tweets but also a fun one, too. Swipe to the right on a tweet to see the full conversation surrounding it; swipe to the left to see replies sent to it. Tap and hold--on a tweet, a hashtag, a username, or a link--to expose contextual options related to that element. With support for services such as Tweet Marker (for keeping you in sync with your device or desktop Twitter client), Instapaper, and more, it's a full-featured Twitter app that's a delight to use.