FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
Fragment - A powerful image viewing suite with advanced metadata info
digiKam - Professional Photo Management with the Power of Open Source
IrfanView - IrfanView ... one of the most popular viewers worldwide.
FastPictureViewer - A hardware-accelerated image viewer for the modern Windows platform.
ImageGlass - You can use Image to view your digital images and photos of many different formats.