ReaddleDocs But you may have documents you don't want to keep in the cloud. This $4.99 app offers a drag-and-drop solution from your computer over a WiFi network to the phone for a range of documents, including Word docs, spreadsheets, PDFs and more. A lot of people seem to use the similar Airsharing tool, but ReaddleDocs has been a smoother experience for me, with more features and flexibility. It comes with 512mb of online storage, syncs with MobileMe and iDisk, and a variety of other Web cloud solutions. It even has a built-in browser that lets you save Web content, making it a possible replacement for bookmark/clipping applications like Evernote, which I still have on my phone and computers but don't use much.
Echofon Pro (formerly called Twitterfon) is my main choice for a Twitter phone client. It handles retweeting seamlessly (without giving you attitude, like its competitor Tweetie). It can show tweets and replies in a conversation format, among other cool features. The free, advertising-supported version is just as good.
Facebook Newly updated, this application is nicely put together, attractive, with intuitive navigation of the Facebook site. Some reviewers say the iPhone version is better than the Web site, and perhaps that is a hint about the mobile future to come, when computers go the way of typewriters and most of us carry the Internet in our pockets.
PicPosterous One-click picture and video posting to a Posterous photo blog page (here's mine), for quick sharing with friends. It will also autopost to other social media sites like Facebook, Friendfeed and Twitter. This app is a snap. Here's an auto-slideshow I posted of the aftermath of a taxi fire near my apartment.
Textplus AT&T used to include 200 free SMS text messages a month with the iPhone data plan. Now it wants you to pony up a monthly fee or pay by the message, making those bits some of the most expensive on the Internet. I don't use enough text messages to warrant paying for a plan, so I'm a la carte. One way to keep costs down is with this free ad-supported application. It gets around the cost by setting up a Web-based group chat with you and your correspondents. Once you text their phone numbers they can reply at no cost to you, even if they don't have TextPlus themselves. With push notification, it behaves like the native SMS client.
AIM Another free alternative to SMS is instant messaging via mobile. I have a lot of work contacts on AIM, gChat and similar networks. This application loads those contacts and lets me chat by phone (again, without per-message charges).
Shorter Oxford English Dictionary At $49.99, this is the most expensive application on my list, and possibly one of the most expensive in the iTunes store. It has more than 600,000 words and definitions, a distillation of the 20-volume O.E.D. into just two volumes. It includes all words in current English from 1700 to the present, and includes a word-of-the-day feature and a randomizing feature for browsing. The best resource for learning the derivations of obscure words.
Shakespeare The complete works of William Shakespeare in a well-designed reader. Follow along at Shakespeare in the Park. Free, from Readdle.