I've used a program called Thotor. It will batch create your thumbnail images and create an HTML index page of the thumbnails linked to the full-sized images. It has options for the size of the thumbnails as well as wether or not to keep them in their original aspect ratio. Found it really handy for making those 'photo gallery' pages for all my digital images as I could just import the generated index page, thumbnails and photos into my website after Thotor had done it's thing.

It can be found at http://www.dominativ.com/thotor/