My favorite image viewer. Free for personal use!

http://www.faststone.org/FSViewerDetail.htm

Changes with version 5.0

Version 5.0 (February 28, 2014)

*Added option "Crop to Fit Full Screen" to the Slide Show tool

*Added larger thumbnail size (260 x 195 pixels) to the "Thumbnail" tab in the Settings (press F12)

*Added shortcut (Ctrl+Alt+A) for "Auto-Rotate based on EXIF Orientation Tag"

*Now it is possible to use the option "Do not resize if image is already smaller than requested size" when batch-resizing images based on one side

*Now you can tag or untag images even when the magnifier is activated

*Other small improvements and bug fixes