DocSets for iOS is a dedicated app for reading Apple's developer documentation on an iPad or iPhone.
It downloads the entire library (iOS and/or Mac), so that it's pretty fast and even works when you have no internet connection.
Requires iOS 5
You can follow me on Twitter: @olemoritz
DocSets is now also available on the AppStore.
By purchasing the App Store version, you can support this project and also get the convenience of automatic updates, not having to worry about provisioning profiles, etc.
Feedback and pull requests are welcome.