"Finally, good digital SLRs are revolutionizing night work - I've seen some available-light stuff that really wows me."
Dont be afraid of ambient (available) light...Like John said above...sometimes the results are spectacular. Some guys seem to think that the scene needs to be flooded with flash bulbs drawing focus only to the locomotive or immediate surroundings (heck...I dont even own anything bigger than a flash specifically for the camera)... sometimes just leave the shutter open and see what happens
ambient (avaliable) light photos below (no flash or other forms of "controled" lighting used)