Despite the fact that the Android 4.0 mod known as CyanogenMod 9 isn't expected to launch until early 2012, its developers are hard at work bringing stable versions of Ice Cream Sandwich to the Nexus S. Programmer Koushik Dutta, one of CyanogenMod 9's developers, noted on his Google+ page that CyanogenMod 9 alpha 11 is "usable as a daily driver," and a thread on xda-developers notes the only remaining major issues are choppy video playback and tempermental MMS behavior. Despite the name, it appears this mod doesn't contain any of the custom CyanogenMod improvements yet.
The Nexus S isn't the only phone getting attention either — a beta Android 4.0 build for the international Galaxy S is available to download on the xda-developers forum. It's worth noting that even though both versions appear to be functional and not missing any major features, there's plenty of posts noting a variety of issues users are having. Problems include some wiped internal SD cards on the Galaxy S and bugs with the contact list and phone app on the Nexus S. So while these releases may be nearly feature complete, they're still not for the faint of heart.