CyanogenMod 9 is probably one of the faster setups for Nexus S on ICS right now, overclocked to 1.46Ghz with Matr1x kernel, if you know a better setup, don’t hesisitate to let me know.
This is a pretty “pure” AOSP ROM with minimal bloatware plus it comes with DSP Manager for those of you audiophiles.
There’s a lot of ICS ROMs out now so I will keep you posted.
For Nexus S, flash ROM, GoogleApps, and Kernel. For Nexus S 4G, flash ROM and Kernel.
Download CM9 ICS ROM for Nexus S: