Cyanogen Mod have come up with their versions for Smasung galaxy s4. They have come up with Cyanogen mod 10.1 nightly for the US T-Mobile version SGH-M919 and the Canadian variant (SGH-i337M) of galaxy s4 two days back. The release for the International version and other variants will be followed at a later date soon. The current releases are working experimental versions of the firmware with not all the bugs cleared. The builds are both in theri nightly stage.
The nightlies of the above versions can be downloaded at the links below.
T-Mobile version SGH-M919
Canadian variant (SGH-i337M)