If you have a 3G iPad you need an app like Download Meter to help you budget your limited 3G plan (I have the $14.95/250 Mg plan). Appshopper and AppAdvice to help you keep track of your apps and to contrast and compare many similar apps, plus gives you wish list for new apps you might want.
Netflix, ABC Player for watching movies and ABC programming. ABC News app is also a good one to have, BBC, USA Today, NPR, and PBS. NBC and CBS have not fully embraced the tablet but they do have apps like CNBC.
For book reading, you already have the iBook app but get
Amazon Kindle, B&N Nook, Stanza, Free Books--why so many? You get a lot of latitude in finding cheaper books, free books, etc.
Print Central. Yahoo Entertainment, Flixstir, Yellow Pages. Photobucket.