mSecure Password Manager: To keep track of all of your account passwords, look no further than mSecure Password Manager ($10, also available for iOS). This app encrypts your passwords to keep them safe in case you ever lose your phone. As a bonus, mSecure Password Manager can generate complex passwords for you, and it lets you sync your passwords across Android and iOS, as well as BlackBerry, Symbian, and Windows Mobile (though not Windows Phone 7).
Webroot SecureWeb Browser: Few security apps are available for iOS through the App Store, but you can find many secure Web browsers that offer extra features to lower your risk of stumbling upon a malicious website.
For example, Webroot SecureWeb (free) will warn you about sites known for phishing and other malicious practices. On top of that, the browser analyzes your search results to determine whether the recommended sites are safe, unsafe, or questionable. SecureWeb ties in to Webroot SecureAnywhere Complete's password manager, so you can reach your passwords from any location. It also includes a couple of nice interface additions, such as a tab bar, so you don't have to switch over to a separate screen to move between browser pages.
iWipe: If you own a jailbroken iPhone, you have a few more security options. One of them is iWipe ($2, available on the Cydia store). This useful utility ensures that the files and data you've deleted from your iPhone stay deleted. The tool writes zeros over the free space on your iPhone's storage, making it harder for someone (for instance, an iPhone thief) to access sensitive data you've trashed.
Firewall iP: Another app for jailbroken iPhones, Firewall iP ($2, available on the Cydia store) lets you decide which apps may connect to the Internet. Firewall iP also permits you to block apps from connecting specifically when your iPhone is operating on a cellular network; that can keep bandwidth-hungry apps from eating up your monthly allotment of data.