Free for commercial use!
It has a good function to make seamless (tileable) textures!
SlowView is good image viewer, but last versions isn’t free 
!!! And last free version (1.0 RC2) for example isn’t support some DDS files !
Now Homepage was changed and You must pay for new version !!! You can download last free version from:
http://www.webattack.com/get/slowview.shtml
Somebody know other, good image viewer (certainly free for commercial use !) ???
I know XnView, but this viewer isn’t free for commercial use !!! Only free for home use :(.
Try Irfanview
http://www.irfanview.com/
It can open practically any media file and is a very efficient viewer. It does batch conversion of images, and can open and view most multimedia formats. I have been using it as my default media player for years.
Dan
definitely Irfanview, that program rocks. I use it all the tiome together with Project Dogwaffle to pass images back and forth instead of saving to files. Then eventually I save with Irfanview in whatever format. Quick resize/resampling too, and great printing controls. I also found that there are great export options in the Thumbnail view (shortcut ‘t’) so you can publish slideshows and thumbnail viewers on html/web. See for example the Javascript slideshow at www.thebest3d.com/dogwaffle (there are also two other slides, using Flash - use the Javascript version)
Irfanview alos has powerful batch conversion and renaming, frame extraction from AVI files, slider to control speed of plyaback for movies (and sound stays in sync)…
It’s free for home use, $10 cash for commercial use. Definitely worth sending him a bill by mail.