Since I've upgraded to Ice Cream Sandwich on my Nexus S, the galaxy live wallpaper - which was part of Android - is gone.
Can I get the exact same live wallpaper for ice cream sandwich? It looks something like this:
You can try to switch your current live wallpapers with the Gingerbread pack the Nexus S came with. This will need your device to be rooted though.
As seen on this topic on xda-developers, you can use Root Explorer (or any other application that can get into the android filesystem, like Root Browser Lite) to switch your with livewallpaper.apk file located on system/app with this one, which contains the stock Gingerbread live wallpapers from the Nexus S, and possibly the one you're looking for.
Also, there's some really similar live wallpapers available on the Market, including one called Galaxy Core 3D LiveWallpaper, which looks almost like the one you're looking for.