Something of a public service announcement; if you haven't noticed you can download the Xcode Developer Tools from the Mac App Store for free now.
This is version 4.1 and appears to be Lion-only. It's about a 3 GB download and one can only hope that Apple will implement the delta update system for Xcode, so you don't have to download the whole package every time there is an SDK change.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20110721055416487