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The Instapaper online service is outstanding at saving online articles for reading later when time is available. The iPad app interfaces fully with the Instapaper service, and is a great reader app for keeping up with interesting topics.
Zite is an app that lets the user build a news magazine from a customized list of topics that makes it very personal. The presentation on the iPad is outstanding, and it gets better over time as favorite articles can be tagged to make sure you get similar items in the future. There isn't an app as good on any platform, Zite is unique.
It may seem odd to have a Twitter app in a list of productivity apps for the iPad, but some of us are Twitter junkies who use it in our work. Tweetbot is a stellar Twitter app that combines a great interface with touch-optimized features that make working with Twitter as good as it gets.