There is a fairly good listing of codes here:
http://www.bearcat1.com/radiout.htm
I especially like the fire dispatch codes. They really help when trying to figure out the situation...
The other day I heard a "D" (Delta) dispatch for Gold Cross and they were told to go 10-40....
Event the ambulance crew questioned the dispatcher. Apparently it was some special deal and the crew was told to contact some supervisor via phone with questions...
Being in the know... It is a great thing!