Haha. Using the list Mike listed I found the mail car, and I can get a replacement mailbag... in fact ebay has them in a group of 10 (cause they will be lost within 5 minutes, I presume They don't have the metal pin required to attach to the magnet on the mailman though. I almost want to buy some replacements even though my O scale stuff is boxed up in the attic... Yeah, I'm anal like that.
In terms of "Operating" cars, I picked up a 3620 at a local shop. The searchlight is supposed to rotate with a vibration motor. This was demonstrated to me at the shop but with my full ZW 275, I don't get any rotation. Still nice to have another lighted car. It's also very heavy.