I'm gradually putting a car in operation on the PER representing every railroad I have had the pleasure of riding on.
Livery currently in operation: B&O, Western Maryland (cheating a bit here-"riding" being a bicycle), PRR, NYC, P&LE, Wabash, Burlington, Santa Fe, UP, Espee, D&RGW (including Narrow Gauge mixed-train).
I still need: Reading (Rambles), Mopac (Colorado Eagle), Western Pacific (CZ), Milwaukee Road (various UP Varnish out of Chicago), Shawmut (excursion), Union RR (excursion), Amtrak (Pittsburgh-Chi-Ft Worth-La-Chi-Pitt).
I'd have to paint&decal myself: Apache RR (White Mountains of Aridzonza), Penn View Mt RR (Blairsville, Pa), Strasburg, East Broad Top.