You can find photos of most of the Classic Metal Works models that have been released over the years here:
http://nscalevehicles.org/resources/models_era.phpYou will also find photos of a number of other manufacturers discontinued models that occasionally show up on the used car market. The list is far from complete, but if you are a member of the N Scale Vehicle Association's Yahoo Group, there are a couple of downloadable PDF files that cover most of the N scale vehicles made in injection molded plastic, die cast and pewter since 1968. Click the Discussion Group link on the NSVA web page to go to the Yahoo Group.