The best way to learn is by looking at examples. To help us learn iOS development better Appsamuck has come out with a unique concept of 31 days of iPhone SDK apps, where they have built one example app for each day for 31 days. Some of these are made just for learning purpose but there are even few full fledged apps, which are also available on app store.
31 examples cover almost all essential iOS SDK topics. Looking at these apps one will surely get to learn many new tricks and techniques about iOS development.
Get these example apps at Appsamuck
Much appreciable effort by Appsamuck team. Thanks a lot guys.