Straighten image is recommended by iPhoneography.com and Life in LoFi
The perfect tool to straighten an image.
Use the slider to straighten an image from your photo library or take a photo with your camera within the app. You can straighten crooked images from -45° to +45°. When you drag the slider a raster appears wich helps you align the image.
*** My bottom line, at $0.99 USD, this app gets high recommendations from me as well. Because of its ease, simplicity and functionality, Straighten Image will quickly become one of my most used photo apps... Life in LoFi ***
***I was amazed at just how quick, easy and simple this app was to use, but the most interesting thing, and more importantly omitted from the AppStore description, is the save photos are upscaled, and so on my iPhone 3G, were saved at full-res.... iPhoneography.com ***