1)   IvanView 2008
View, Browse, Edit and Convert Digital Images. It's capable of viewing more 60 image formats and has unsurpassed conversion capabilities in 15 of the most popular formats. You simply must see it!

 2)   Smart Converter CL 1.9.24
Smart Converter CL is a heavy-duty command line batch image converter that supports 88 image formats and works with Formula 1 speed. Conversion and batch processing (resizing, cropping, etc.) are done through command line only (no GUI)!

 3)   Onekit Texture Converter 1.0
Onekit Texture Converter is a freeware tool for 3D game developers. This tool converts PNG format images to JPG images, taking into account the alpha channel presence. However, it's not all this tool can perform.