FX Photo Studio HD has been a staple on my iPads for a while. The US$1.99 app from MacPhun, which is used to edit and apply a variety of effects to images, has recently been updated to version 5.0, adding more effect filters and now including support for Retina displays. The update also improves performance on the iPad mini and officially provides support for iOS 6.
If you're not familiar with FX Photo Studio HD, it's well worth the investment if you want to jazz up your photos, crop them or adjust the colors. Thanks to a well-designed UI, the app is a snap to learn and use.
Images are imported by tapping a "load photos" button (it looks like a flower) which then displays three buttons -- one to load from your iPad photo library, one to import images through a Camera Connection Kit, and one to take a photo using the iPad camera. Once an image is loaded, it is displayed with a palette of tools across the top and a scrollable list of effects on the right side of the screen.