Sparkle
This one is for all the Cocoa developers in the house (when I say 'Core' you say 'Data'!). Isn't writing your own auto updating procedures for your applications a drag. Yeah, I though so.
Luckily, there is Sparkle! Andy Matuschak wrote up this little marvel that will allow you to add intelligent auto updating to your Cocoa applications in 5 steps. The price is right as well, as in free.
Why not give your applications a little Sparkle?