DropJPEGResize is an utility that allows you to batch resize multiple JPEG files by simply dropping them to the application's icon. It can also rename and index your files.
JAKE Beware, I didn't test this fully, but its not a DROP app at all, and when i choose a folder of files in its default settings (changed nothing) it processed my files in to the abyss...
MACBUDDY Does seem to work, but not as a drop App. You have to open your file from 'File > AddFile...' menu item.
Also, it changes the resolution of images to 72 dpi (most 'reducers' do), although it seems to do a fair job using 'Relative' Width/Height if the numbers are the same (ie:50/50).
Oh, and work with copies, if you need to preserve originals for archiving. (Version 1.0a1)