Iconverter was written originally as a developer tool to create ICNS files from anything dropped on it, now it has evolved to support icns, gif, jpg, png, bmp and tiff exporting--and batch conversion. The source code is available.
What's new in Iconverter
I received a lot of interest in this program being made universal. It hasn't been actively developed in half a decade. Because of this interest I am releasing this v0.9 version that includes updated intel compatible libraries and is compiled as a universal binary. I have no intel machine so could not test it, if any issues persist feel free to email me but be forewarned that i do not have much time to devote to this project.