One of the more uncommon American OO items was just seen on eBay this past week, a Nason box cab "diesel." This model was introduced in 1939 and was also featured in their 1940 catalog, and is actually an electric loco (New Haven prototype) minus pantographs in sand cast bronze. The model was discontinued with WWII but was later also produced by Ultimate.
The link is here, take a look at the four photos while you can. It sold for over $150.
UPDATE: Of course, that link is long dead but thanks to Dick Gresham I have a couple photos of another Nason box cab. This example is lettered for the Rock Island, which seems appropriate as they had a number of diesel locomotives of unusual designs. This particular model is built up in a way that matches the model in the 1940 Nason catalog (photo here) very closely. Dick commented,
UPDATE: For photos of two more nicely built examples of this model see this article.