The official Android 2.3 Gingerbread is available for Samsung Galaxy S. It is available only in some countries/regions for now. The update is/should be available through Samsung Kies.
Since I still do not see it in the list of updates, I decided to look around for leaked versions. So, here are some:
here and the accompanying video here.
After installing the new ROM, the phone will have to be rooted again (or here). I used instructions from Nikademus thread.