XCode 1.5 comes with an improved code completion system called CodeSense. CodeSense works great with Java and Objective C but, by default, some frameworks aren't indexed, so code completion doesn't work for them.
Apple explains on the XCode release notes how to enable CodeSense for these frameworks and provide a shell script that enables all of them. Unfortunately, I'm lazy and I wanted to test Cocoa bindings with an application... So now you can do that with a GUI!