Day One is a highly regarded personal journal for the iPhone.
Version 2 is just out, comes with a lot of new features and controversy (specifically the removal of dropbox as the sync service).
To get this app for free:
1: Open the Apple Store app on your iPhone (not the app store app).
2. Tap the "Stores" button at the bottom.
3. Scroll to "Get it the way your want" section
4. Swipe across 2 times until you see "Keep a beautiful Journal"
5. Tap, It should open the app store.
6. Tap Redeem up the top right
7. Free app
Thanks