Quick note: I’ve updated the iTunes 5/6-style window code (Polished Metal, as it seems to have been named). It’s now an NSWindow subclass, so you can just drop the files into your existing Xcode projects, make a quick change in Interface Builder, and your windows will be polished metal. Not tested much, ymmv, etc.
Get the new source from the Cocoa Source page. I know that many of you are already using the code as-is in your applications, but I’ve had a few requests for an easier-to-use version, so there you go. Enjoy.