Here is Shrink O'Matic, my new AIR application!
Simply drag and drop images on it and they'll be resized as you wish.
More info on the project page...
I've also set up a new projects' page listing AIR apps and more.
Concerning the source code, it's not available but you can find parts of it in a brand new Google Code project where I've added (and I'll keep on adding) classes I use.