I have added a small Cocoa app call DDRetinaResize to my retina extensions project on GitHub.
The app is nothing special, it simply takes a folder containing images scaled and named for the retina display as input and populate a destination folder with scaled-down and renamed images.
Assume you have a folder filled with images named firstname.lastname@example.org or email@example.com and scaled for the retina display (so twice the size of the original image). The app will remove the @2x extension to all images and scale them down half. It will then copy the newly created images to your destination folder.
Again, this is nothing special and the code is far from being nice, but hey, I had a folder of 500 retina images to resize and rename and it only took me 2 seconds ;)
The project is on GitHub here.