When it comes to model trucks, the two biggest names are probably Tonka and Buddy L. Tonka, founded in 1947 as Mound Metalcraft, has long been famous for its steel construction toys, including trucks, dump trucks, wreckers, semis, cranes and tractors. The company changed its name to 'Tonka' in 1956, which supposedly meant 'great' in Sioux. Tonka was later bought by Hasbro.
Buddy L. was founded by Fred Lundahl, who made steel toys in his spare time for his son and his son's friends. In 1921 his company, the Moline Press Steel Company (later Buddy L.), began making toys full time. They made trucks, cranes, cars, and trains, mostly out of pressed steel (and wood during WW2).
Other companies like Marx, Structo, Keystone, and Kingsbury also made pressed tin and steel trucks, mostly inspired by Buddy L. models, which are typically the most valuable.