So you want to edit your photos but don't want to spring for photoshop, who can blame you at five hundred bucks a copy.  Image Magick operates similar to photoshop with layers, images can be used or saved in just about any format that exists.  Just want to flip a photo, its a no brainer, just some minor adjustments there all here at the click of a mouse.

From Source : Every feature and user interface element was designed to be immediately intuitive and quickly learnable without assistance. In order to handle multiple images easily, Paint.NET uses a tabbed document interface. The tabs display a live thumbnail of the image instead of a text description. This makes navigation very simple and fast. The interface is also enhanced for Aero Glass if you are using Windows 7 or Vista. Click the blue arrow to download.