Samsung Galaxy S4, released a month back receives the stock firmware labeled I9500ZCUAMDG. The firmware is only for CHN (China) region only. The firmware is expected soon to hit S4's from other regions as well. The update is to be done using Odin. The current version of Odin that to be used for galaxy S4 is Odin 3.07. The stock firmware is based on Android Jelly Bean 4.2.2 and brings all new features that could be from a vanilla build. The firmware, Kernel and Odin download links are given below.
About the firmware
Region: CHN (China)
Build Date: 24.04.2013
Android: 4.2.2 (Jelly Bean)
Firmware : http://hotfile.com/dl/204475706/aa7ff36/Samsung-Updates.com-GT-I9500-CHN-I9500ZCUAMDG-1366762450.zip.html
Kernel : http://hotfile.com/dl/204475720/8e82fcc/Samsung-Updates.com-KERNEL-GT-I9500-CHN-I9500ZCUAMDG-1366762450.tar.html
Odin 3.07 : Download