XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!
Photoscape - high quality photo editing software, that enables you to fix and enhance photos.
IrfanView - IrfanView ... one of the most popular viewers worldwide.
Pixelmator - Pixelmator is an image-editing application for Mac and iPad.
JPEGView - JPEGView is a small and fast viewer/editor for JPEG, BMP, PNG, GIF and TIFF images.
ACDSee - ACDSee is an image viewer that uses very little system resources, and it has a small, sleek size that won't take up much space on your system.