http://www.smashingmagazine.com/2008/10/02/15-useful-batch-image-processors/

Here is a great list of software you can use. I'm previously used BIMP and it works great. Though this list has some clever tools, some can even be used to manipulate the images, and provide snazzy effects.

One of the mac ones, allows you to create different presets, so creating groups of 150px, 300px and 500px images is a simple task. definitely a good app for everyone that creates thumbnails.

I feel that in some cases, though Photoshop can batch these images, its really overkill, especially when I want to *USE* photoshop, while i'm batching some images.

so, enjoy! :thumbsup: