I have created a GUI application (based on signapk.jar) which sign multiple APKs and ZIPs very quickly, in one clic!
1. Extract Archive 'Sign+.zip'
2. Launch 'Sign+.exe'
3. Choose files (APKs...
Here : http://forum.xda-developers.com/showpost.php?p=26215624&postcount=3758
I don't know if I make this for OS X and Linux too! Maybe in few week!