Excelsior Park (especially chronographs), Angelus, Buren, Record, Leonidas, Helvetia (not the PW brand of Louis Brand Freres, aka Omega), Phenix. Technically speaking, also Blancpain, Lange & Söhne, Vulcain and probably Universal Geneve (most or all of the modern versions are reincarnations after the original closed down).
Bulova mechanicals from before the 60's are excellent. Technically not a "lost" brand (they were sold to Seiko in '07), but they haven't made their own movements for decades.
Pre-60's Benrus watches are excellent as well.
Certina, not lost but I don't think they make their movements any more, and Eska. Eska didn't make their own movements, but they certainly assembled some lovely pieces including split-second chronographs and cloisonne enamel dialled dress watches.
A forum community dedicated to watch owners and enthusiasts. Come join the discussion about watch collections, displays, watch winders, accessories, classifieds, and more! We welcome all manufacturers including Casio G-Shock, OMEGA, Rolex, Breitling, Rolex and Tudor, Seiko, Grand Seiko and others.