XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!
digiKam - Professional Photo Management with the Power of Open Source
JPEGView - JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images.
IrfanView - IrfanView ... one of the most popular viewers worldwide.
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
splash image viewer - A borderless window image viewer for splashing images on the screen.