Andy Matuschak is the author of Sparkle, a framework to help with software updates of Cocoa (OS X) applications.
True self-updating–no work required from the user. Supports bundles, preference panes, plugins, and other non-.app software. Deep delegate support to make Sparkle work exactly as you need.
Sparkle is used in many familiar OS X apps including Textmate, Evernote, Adium, Handbrake, among many others.