Here is a free and fast image viewer for quickly viewing image file formats, including *.bmp, *.jpg, *.tga, *.png, *.dds, *.vtf, and *.stf. You can view an image's alpha channel. Scroll the mouse wheel to flip through images in the same directory. Press the mouse wheel to toggle full-screen mode. You can associate your image files with this program, and open them instantly in the viewer.
http://www.leadwerks.com/ccount/click.php?id=35
http://www.leadwerks.com/ccount/click.php?id=35