In need of some shiny new Cocoa source code? Then allow me to recommend MGScopeBar (which is actually from a project I started months ago, but I’m only just releasing it now so it’s new to you).
MGScopeBar provides a scope/filter bar like you’ll find in Mail, the Finder (in the Find/Spotlight window), iTunes and elsewhere. It requires Mac OS X 10.5 (Leopard) or later, and it looks like this:
It uses a delegate system very much like NSTableView’s data-source, and supports all kinds of snazzy things like optional icons for buttons, an accessory-view at the right side of the bar, button-groups which support single or multiple selection, and more. It also has a very cool feature which I call Smart Resize - take a look at the demo movie to see how it works.
Lastly, if you’re feeling particularly grateful, may I be so bold as to mention the donation link on my Cocoa source code page and/or my rather nifty iPhone application, Favorites? Yes, I think I may.