I subscribe to the xkcd school of password philosophy. Multiple words are a big pain to type, but they offer good security and memorization. If you prefer to use shorter codes, especially for touch-input devices, consider Mnemonizer (US$0.99). It provides a novel security approach, enabling you to obscure your codes in plain text.
The app works by providing a random data generator, which surrounds your PIN codes and passwords with similar-looking elements. You pick the pattern and enter your custom data by editing whichever cells you desire.
You can build your item in a simple line, as a skip pattern or even as a zig-zag. However you hide your information, the app provides a camouflaging environment to surround it. Once created, add a context name and your stored information is ready to use.
Aesthetically, I found the interface to be gorgeous. There are some absolutely lovely design choices that make the app a pleasure to use.
Less pleasurable, however, is how easy it is to reset data for any password. If you tap the scramble option, your cells reset, replaced with random values. All stored information is lost. Unfortunately, you don't need any special password or privileges to do this, so anyone randomly picking up your phone can really mess up your saved information. The app really needs a passcode to enable any data modification for existing mnemonized items.
I don't think I'd use this app to store long values like credit card numbers and I suspect I'd use the same visual sequence across every PIN, which would introduce its own vulnerability. Once anyone figured out one of my PINs they'd have access to all of them. Even if this particular app doesn't really work with my personal style, I suspect it will be valuable enough for those who can leverage its clever approach.
That said, I look forward to seeing what other apps the developer creates. I really liked supporting elements even if the main feature isn't really my thing and I'd love to see those great design touches in other apps.