IrfanView - IrfanView ... one of the most popular viewers worldwide.
ImBatch - ImBatch is a batch image processor with a nice graphical user interface.
XnView MP - XnView is a free software that allows you to view, resize and edit your images. It supports more than 500 different formats!
Batch Image Resizer - Resize, crop, shrink, flip, exif-rotate, convert, enhance, process multiple pictures and photos with professional software! 120+ Actions, 30+ Image Formats
FastStone Image Viewer - FastStone Image Viewer is a fast, stable, user-friendly image browser, converter and editor.
Phatch - Phatch = Photo & Batch!