Unlike many of the iOS 5 features you can get right now, enhancing your camera app or editing photos directly on your iPhone does not require jailbreaking your device. There are two applications that can be installed from the Apple App Store that provide the functionality of iOS 5 Camera and Photo app improvements and more.
First we'll start with taking pictures and recommend the Camera+ app for $0.99. Not only will Camera+ take better photos than the stock Camera app, it adds features that are not even included in iOS 5. Open the app and you'll see grid lines that help compose the shot and a simple zoom slider on the right.