Apple released xcode 4 with iOS sdk 4.2 on 9th of March 2011.
The xcode, ladies and gentlemen, is no more free! Like the old days (almost 1 day old) sdk was free. You could download it and develop whatever you want. However to upload the file to Apple iTunes you needed to have a developer account which cost around 99$.
If you want to continue with developing on xcode for mac or iphone, you need to purchase the xcode 4 release from Apple.
Cost: Xcode now costs you 4.99$ (I hope it will make them rich! woo!)
You can download xcode via apple store here
: Apple xcode.
Update: You need to search for xcode in Apple store and then download it. The bugs in Apple system never end!