This page contains some  great open source controls and examples  of Cocoa/Objective-C source code from Mac developer Uli Kusterer.

Includes: MacScare, MachO-CFM Glue, “Made with Cocoa” buttons,  NiftyFEatures, ShadowCopy, UKCrashReporter, UKFeedbackProvider, UKDirectoryEnumerator, UKDistributedView, UKDockPregressIndicator,UKDockableView,UKPrefPanel, UKKQueue, UKDocumentController, UKFontMenuController, UKIdleTimer, UKSyntaxColoredTextDocument, UKSpeechSynthesizer, WindowFlipper,VerPack, UKToolBarFactory, UKXMLPersistence, UKXatteMetadataStore, UKLoginItemRegistry, UKFilePathView,NSWindow+Fade, UKCustomWindowFrame, UKProgressPanel, UKDebugNames, UKSOundFileRecorder,UKHelperMacros, UKTurboExport,UKDiffView.

View the page here