Day One is a journal or diary application for the Mac, iPad and iPhone. It syncs beautifully between devices. It is a universal application for the iOS devices and it cost $1.99 for the iPad/iPhone. The Mac version is a little more expensive at $9.99 but worth every penny. It offers password protection on both iOS and OSX platforms, it uses iCloud or Dropbox to syncs notes/entries between devices.
In my opinion this is the best journal application in the app store.