Here are a couple of neat iOS applications for the paranoid (kidding!) & security inclined.
iPGMail (currently $1.99 on the App Store) is the best OpenPGP application I’ve tried on Apple’s platform. Even within the somewhat restrictive limitations that Apple has created for application developers this particular application does everything it can to be user friendly. I would highly recommend this to anyone that wishes to send signed/encrypted e-mail from their iOS device.
Like what iPGMail does for e-mail, Threema (currently $1.99 on the App Store or $2.20 on the Play Store) does for instant messaging. This neat little App is very similar to BlackBerry Messenger or WhatsApp but provides additional levels of security and verification so you know exactly who you are talking to. For example you will get two verification dots (out of three) if the service has been able to confirm that the person on the other end is using an e-mail address or phone number in your personal address book. They get all three dots if you have scanned the unique Threema QR code on their phone in person.
If you use KeePass on your desktop then this application is a must. MiniKeePass (currently free on the AppStore) lets you take your KeePass database of passwords with you on the go while still being protected by strong encryption – so even if your phone is stolen your passwords should still be safe. The interface is pleasant to use and lets you easily copy passwords for pasting into websites.