Old thread, but seeing as image optimisation never dies...
Enter
smush.it!
It's a ridiculously simple image optimiser, 1 click optimisation, it works as a firefox plugin and gives completely lossless compression. You just go to a page, click the smush.it button and it takes you to a page where you can download the optimised page images in a zip file. They even have an API if you're that way inclined!
Regards,
Darryl