Manufacturers

Märklin	Zthek	Pennzee
Micro-Trains Line	Hay Bros. Garage	Railroad & Co.
Freudenreich Feinwerktechnik	Micro Structures	IBL
Krüger	Bachmann westmodel	Micron Art

These are firms I've had contact with. There's a more comprehensive page of manufacturers at Do it Yourself in Z-scale