One of my favorite iOS apps, Day One, is free this week as part of the App Store's 5 year anniversary promotion. The iOS app is normally $4.99 and really is one of the nicest apps I have ever used.
You can read my review of Day One, but at the price of free this week, you don't have much excuse not to grab it.
There are other apps in the promotion which you may like, and Tools & Toys has a lovely roundup.