A new custom Ice Cream Sandwich ROM for Samsung Nexus S is floating around. This build is purely modified from the Android Open Source Project (ASOP) and CynagenMod 9 ( ICS vesion ). All major features are present and most of the annoying bugs are fixed.

ROM Manager and modder Koush has been working on this custom CyanogenMod 9 mod for Samsung Nexus S and has finally released the Alpha build 11 of this mod.

Installation and other instructions are provided on XDA-Developers forum here.