Freight Car & Passenger Car Kits you have built that you feel build into great models. - Model Railroader Magazine

NP2626 .... This continues to be an interesting thread. It looks like you have edited the first post to include some of the ones mentioned by other contributors. There may be some that did not get edited into that post. Perhaps, I just don't see them there, but check for kits by MDC/Roundhouse, Proto 2000, and Walthers. 

Central Valley was mentioned regarding their stock car kit. The old Central Valley kits were wood freight car kits, and they made nice models. Central Valley also produced a line of premium quality trucks which were the favorite for many years. 

I can recall some of the old kit makers of HO kits of roughly 50 years ago. .......

Varney made some nicely painted metal freight car kits. They were one of the early makers of plastic kits. 

Athearn also made nicely painted metal freight car kits, and they also were an early maker of plastic kits. The plastic kits evolved into the popular blue box kits. 

American Beauty lines made a line of nicely painted smooth side passenger car kits. 

Herkimer / OK Models made a line of extruded aluminum passenger car kits. Another owner of this company has made them in more recent years. 

Ulrich models made freight car kits using die cast metal and wood. They also made highway trucks.

Mantua made extruded aluminum passenger cars based on Budd prototype. They also offered freight car kits. 

Silver Streak made freight car kits with wood and die cast metal.

Tenshodo produced some imported brass freight car kits in addition to their popular brass locomotives and passenger cars. 

JC Models made a line of heavyweight passenger car kits with metal and wood. 

Walthers made a line of heavyweight passenger car kits with metal and wood. 

Ambroid Models made a line of wood passenger kits and freight car kits.

Quality Craft Models made a line of wood freight car kits.