Another great free option is XnView. Along with Irfanview it's probably the most recommended image converter and viewer, but I prefer XnView by a good margin. XnView supports more formats (over 400 for viewing, 50 for saving to), is more frequently updated, has decent filter and image adjustment functionality, an image browser, tabbed interface, is highly customizable, has great screen capturing system built-in, powerful batch processing, and a lot more.
Free download here: http://xnview.com/en/index.html
Feature list: http://xnview.com/en/features.html
Supported format list: http://xnview.com/en/formats.html
Regards,
Oshyan Greene