Okay, I know you dismissed using Photoshop, but really it is very easily done when using the program. You can make a key (like F3) a shortcut to doing an "action". For your example, you can keep hitting F3 after you define your "action" for all your photos and they will be smaller. I know you don't like Photoshop, but here is a link in case you want to pursue:
http://adobedoc.kanisasolution.com/Photoshop6/c19au2.htm