For a device with a 3" screen, the iPhone has a pretty impressive resume: Phone, map, camera, sketchbook, dedicated Doodle Jump playing machine. And for $1, the newly revamped Ruler 2 app makes it a pretty decent measuring thinger, too.
Ruler 2, an overhauled version of an apparently less-good Ruler 1, offers a simple, functional ruler that you can drag to measure things smaller than the size of your screen. Measuring things that are longer than your iPhone (or your iPad—it's a universal app) isn't quite as precise: you swipe the ruler to extend it a length and then physically move your iPhone, keeping track of where the left side of the screen should be with your finger. It sounds kind of confusing, but a nice how to video that plays when you first launch the app brings you up to speed quickly.
Measurements can be labeled and saved to a folder, so you don't have to mark them down elsewhere, and overall the app has a nice, straightforward design. If you think you'll ever need to measure something small with accuracy, or measure something slightly less small with slightly less accuracy, Ruler 2's worth your dolla. [iTunes]