IrfanView is also free and supports most Photoshop plug-ins. It comes per-configured with many free ones.
I know of a few local universities that use it for their image editing classes.
I've also used it on websites I've taken over that had all their thumbnails saved at 100% quality. That was using it's batch mode capability. Saved me a LOT of extra clicks! And of course saved him lots of bandwidth too :-)