Thumb-nail generator

I have searched google and here but cant find anything, I need a program which I can just give some photos to (about 20 at a time) and it generates thumbnails ate a certain dimension, I dont mind if it just shrinks the whole image or just gives a clip of it, if anyone has or knows of such software could you put a link here.

Thanks,

P.S, it woudl be better if was free or has trial :hugegrin: