11. Phone Trace
A GPS-centric app ($4.99) that lets you pinpoint a phone or the location of a child, spouse, etc. carrying a phone running the app. It does not include any further security features (remote lock or erase, for instance) but doesn't seem to require any sort of subscription.
12. TrackMe FindMe
This free app is backed by a subscription service (which, strangely, you have to register to learn the price of) that costs $24.99 a year. You can track the location of your phone, or those belonging to friends and family using TrackMe FindMe, via a web console.
13. Call Your Phone
This technique won't help you retrieve a stolen iPhone, but if you've lost your phone around the house or office, it'll do fine. Just call your phone number and, unless your ringer is off, you'll be able to track your phone to between the couch cushions by following the rings.
14. Make Wallpaper with Contact Info
Though a few apps above offer a similar thing, you can create a wallpaper with your contact information for free. Use your favorite graphics program to create a wallpaper (320 x 240 pixels on older iPhones, 960 x 640 on the iPhone 4) with your name, email, alternate phone number, etc. Then sync the image to your iPhone and set it as both the wallpaper and lock screen. This won't foil a thief, but it could help you get a lost iPhone back.