[UPDATE] FastStone Image Viewer 5.2
The best free image viewer (IMO).
Changes:
Version 5.2 (September 24, 2014)
*Now you can copy and paste objects in Draw Board
*Added "Zoom at Center/Mouse Position" to the Settings
*Added "Smart-Filling" to the advanced options (Resize tab) of the Batch Convert tool
*Added Fit Width (Shift+W) and Fit Height (Shift+H) to the Zoom menu
*Improved the Copy/Move to Folder tool. Now you can press 1 to 9 to select a pre-defined destination folder
*Many other improvements and bug fixes
http://www.faststone.org/FSViewerDetail.htm