Model buses have long been a popular genre of childrens toys. The main makers in the 20th century were Corgi, Dinky, Matchbox, St. Petersburg, Royal Coach, and Tootsie Toy. Some Japanese and other Asian companies also released models similar to those of Corgi and Dinky.
Model buses were made of lithographed tin, pressed steel, aluminum, plastics, and even a few in cast iron. Look for condition, but also for real-life bus lines and city names stamped on the buses. Pressed steel, lithographed tin, and cast iron model buses generally fetch the highest prices.
Another subgenre of this category is bus banks, which were made by some of the same companies, and are still popular today. Most are either tin or pressed steel, and about half are from western companies like Corgi. The rest are from Asian companies.