On Real World I saw an interesting new app called RB Package Maker Studio. If you are planning to release something on the Mac App Store, you should check it out. You can easily setup your app and reuse the same values for future versions. It does the code signing, the plist changes and packaging for you.
Of course with new sandboxing requirement on the Mac App Store soon to come, please make sure your app is working well as Cocoa app.
It was nice to see this app in Orlando at Real World conference demonstrated by Ingo Molitor. For more details, check the website.