VarieDrop generate multiple-size-images in one operation. The process is started from the drag-and-drop or "Sent To" menu. You can shrink and append string to output file name.
This was the only free-app I could find that allows me to:
* Resize a picture by setting a max file size
Example:
* I want a set of pictures to be 64kb in size
* Just drag and drop onto VariDrop and done!
Every other app I looked at allowed you to resize based on height & width. JPG quality, etc. but not size of the file.
And its free!
Cons
Interesting user interface but it works for the cost.
Summary
Great app for resizing by filesize. It does a lot more as well.