Free editor for PDF documents. Complete editing of PDF documents is possible with PDFedit. You can change raw pdf objects (for advanced users) or use many gui functions. Functionality can be easily extended using a scripting language (ECMAScript).
JPEGView is a lean, fast and highly configurable viewer/editor for JPEG, BMP, PNG, WEBP, TGA, GIF and TIFF images with a minimal GUI. Basic on-the-fly image processing is provided - allowing adjusting typical parameters as sharpness, color balance, rotation, perspective, contrast and local under-/overexposure.
UniView is an universal image, text and multimedia viewer (and editor). It supports many formats, contains plugin technology and a few interesting features (like javascripting). Distributed under GPL v2 :-)