American Models
Considered to be the largest manufacture of S scale products.  American Models has everything from steam locomotives to track.  Their website is their full line catalog so it is a must visit.  Be sure to check out their latest offerings. 

S Helper Service
Established in 1989, the company prides itself in developing and marketing high quality Ready to Run "S" scale model railroad equipment.  A visit to their website is a must!  Be sure to sign up for their quarterly update, The SHS Update.

The above list is a work in progress with many more links to come...  Manufacturers, feel free to email us your information.