Count my vote for Lightbox!
It’s pretty easy to integrate, and the results are “fantastic” for 99% of cases.
Two minor things to keep an eye out for:
1.) Don’t assume that just because Magento gives you options for “Thumbnail”, “Main Image”, etc, that this is the limit. After setting up Lightbox, just keep adding images - LB will “pick them up” and add them to rotation. I have a product with 16 images, and they work fine.
2.) If you have trouble finding “page/html/head.phtml” - its location is NOT specified in the instructions, it’s actually sitting here (if Magento is installed as root):
P.S. If you’re not a fan of LightBox, there are other “gallery” scripts out there (FrogJS, etc.). You’ll need some PHP knowledge to integrate them, though!
Hope this helps!