Camera+ for iOS
While the iPhone 4S' camera hardware is pretty great for something you always have in your pocket, Apple's simple shooting software has left room for dozens of great apps to spring up.
The winner in my book is Camera+. It has some great filters and borders, nice cropping tools and (most importantly) is super fast to launch and shoot. It can import existing photos on your phone, and with built in social media sharing and super quick access to the Camera Roll, getting images out of Camera+ is as easy as a few taps.
A few years ago, the developers made news when the app got tossed from the iOS App Store for using the volume up button as a shutter button. Famously, Apple added this feature in its own app in iOS 5. It's this kind of forward-thinking that keeps Camera+ on my home screen.
It's currently on sale for just 99¢ on the iOS App Store.