ACDSee Camera Flash lets you instantly correct your underexposed photos using patented LCE technology. Patented LCE (Lighting and Contrast Enhancement) from ACD Systems International Inc is the same driving force behind the Lighting tool in the ACDSee photo editing products. It adds natural-looking illumination to the dark areas of your photos while still preserving contrast and detail using advanced image processing algorithms from ACDSee.
This app usually retails for $0.99/£0.69 but at the time of writing, in the US and UK app stores, it is free. Click here to download.