National Association of S Gaugers (NASG)
The national standards organization for S-scale modeling. The web site has lots of useful information for both the beginning S-scale modelers and the more experienced ones. The "S Resources" page on that site contains a listing of links to all current "S" manufacturers, and is a great place to start exploring the world of S-scale modeling.

National Model Railroad Association (NMRA)
The national standards organization for model railroading in general. This web site also has lots of good information, especially if you are new to the hobby.

American Models
This company produces very nice looking S-scale engines, freight and passenger cars, track, and parts.

Lionel
Lionel used to be A.C. Gilbert's main rival. However, when the A.C. Gilbert company declared bankruptcy in the late 1960s, Lionel bought American Flyer. However, Lionel went bankrupt about a year later. A new Lionel eventually re-emerged, and that is the one that is currently active. They own the American Flyer brand, and they continue to produce S-scale products under that brand name.

Scale Trains
In 2012, S-Helper Service, manufacturer of high-quality S-scale engines, cars, and track systems, announced that it sold its production tooling to MTH Electric Trains. In 2021, MTH Electric Trains closed due to the principal owner's retirement. Scale Trains has bought the tooling and rights to produce the S-scale product line. It will take a few years for them to evaluate what they received, and to start production, probably starting with a re-run of some of the existing tooling, and maybe in the future some new products. Scale Trains also makes high-quality scale models in other scales.

Papa Ben's Train Place
This is a local, full retail store dedicated to model railroading. They occasionally carry S-scale items, however, you can special-order through them, and they do have lots of general model railroading items. They are a Lionel and M.T.H. authorized dealer.

Des Plaines Hobbies
Primarily focused on S-scale items, this model railroad hobby shop in Illinois carries brass equipment, kits, decals, parts, and structures. They own "S Scale America", and "Pacific Rail Shops".