The GC options should be documented. They are:

-XX:+UseParallelGC, which has been around since 1.3.1 or 1.4
-XX:+UseSerialGC, which is new for 1.5.0
-XX:+UseTrainGC, which will go away in 1.6 I believe
-XX:+UseConcMarkSweepGC

These options (except UseTrainGC becuase it has been removed and not available for JDK 7) are already documented:

http://www.oracle.com/technetwork/java/javase/tech/vmoptions-jsp-140102.html