There are three on my wish list, two of which are going o be close to impossible to do. I grew up in Philadelphia and rode the trolleys, buses, trackless trolleys, and subways a lot for public transportation. I would love to model the trolleys and subways from back in the early to mid 60s, when it was PTC instead of Septa. The trolleys and buses used a cream colored top, a green bottom, and a red stripe in the cream just above the green. While the subways were most polished aluminum, I also remember the older ones - probably from the 50's but still in use - that had a maroon paint scheme. Bachmann does have the PTC trolley in HO, and I might end up ordering it just for a small display. If I could find the subway cars I would definitely end up with that spare layout (they ran the same cars on the elevated line so I could build a portion of the city that way - modeling underground cars does seem really interesting).
The third one, and I am considering this, is Amtrak from Phase I or Phase II paint eras. I used to take Amtrak to college in Kansas and home from the Army, but I also took it from Philly to Trenton to see my first girlfriend before I got a driver's license.