XResizer

XResizer screenshots

It helps you easily resize @3x and @2x images into low-resolution images.
Main Window
XResizer 1.0 : Main Window

Alternative downloads

iPhoto
9.6.1
FREE
Note: This is no longer an actively developed application.
Resize Sense
2.3.11
This app helps you resize, crop, rotate, and flip your pictures.
SP Resize
1.1
Intended to be used in conjunction with Quicksilver.