Southern Pacific (Scarlet red nosed and gray, Halloween and Daylight), Santa Fe, Union Pacific, Burlington Northern, Pennsylvania Railroad, B&M, B&O, C&O, C&NW, Rock Island, Great Northern, MKT, Mo-Pac, NYC, Saint Louis-San Francisco Railway (SSW), SP&S, T&P
With thanks to Paul, there's no need for me to repeat those, but New Haven and Maine Central units would be nice. I think the New Haven used these as a basis for their FL9s, which are similarly designed, but I can't remember so even an FL9A would be cool.