The Nexus S will be running Gingerbread (Android 2.3) and support Near Field Communication (NFC).
Since 16th December it is available in the US. The release date for UK is 20th December. In Germany rumors say it will come to the stores in March 2011 with Android 2.4 preinstalled!
(source: mobiflip). (Why so late?)
Gingerbread brings strong performance improvements and also comes with a SIP integration, Google Voice ready.