Text sources - Online books

Archive.org - Many library links
Hathitrust - Academic Library
Kalmbach Memorial Library - Not much online.
Linda Hall Library Collection - Look for digital collections.
Linda Hall Library Railroad Collection - Includes books and decently sized photos.
Railroad Heritage - decently sized photos.
Railroad History, Railways, Locomotives, entrepreneurs, business history 19c American, Jensen

Clubs and individuals - Narrow gauge

Arroyo Mining RR On30 ‎(Deer Creek and Laurel RY)‎
Australian Narrow Gauge Web-Exhibition
Carthago Salon - Model railroading (Japanese)
Diamond Springs & Western - HOn3, microlayouts and photos
Don Hamilton's On30 Canadian Style - Nice example of using an automated cutter for car sides
HOn30 Home Depot
John Ott's Old-Time Railroad Models - Some lovely stuff here!
Model Railroad World - Japanese site
Narrow Gauge Model Railway Exhibition
Oklahoma Narrow Gauge
The On30 Information and Resource Center
Pacific Coast Air Line Railway - Big On30 railroading - great stuff!
Scott Robertson's ND&AC - On30 layout with fabulous paper and foam core buildings
Troels Kirk's Coastline RR - Awesome!
VoieMetrique - Zafra On30 Cuban Railroad

Clubs and individuals - Standard gauge

Bay Area Garden Railroad Society
Daryl Huffman - Great source of how to DVDs!
Honshuu railroad - Phillipine prototypes and model railroad (Japanese/English)
Housatonic Railroad Home Page
John Bruce's Los Feliz and North Western Railroad (HO)
O Scale Kings
Proto 48 Modeler - Great stuff including making your own drivers
Wolfgang Dudler's Westport Terminal RR

Freight cars

NorthWest RailPics Freight Car Archives
PRR Boxcar diagrams

How to

The Cane Railway (Tramline) Modelling SIG
Charlie's Railroad Page, layouts, timesaver and tips
CLAG (Central London Area Group) - Awesome how to and info and keeps improving!!!
Dutton Bay Tramway, excellent link, good casting how to
Guerrilla guide to CNC machining, mold making, and resin casting
Layout Design Special Interest Group
Missing Links Article Adam Wilder Painting and Weathering
RMWEB - massive British model railroad forum
Scale Models and History of the Keweenaw - Huge amounts of drawings and how-to *
Wiring for DCC by Allan Gartner

Live Steam

Eureka 4-4-0 1875 Baldwin


Bill's Train Shop (B.T.S.)
Boulder Valley Models - makers of resin kits in O scale
Builders In Scale - Check out CC Crow's Clinics!
Euro Rail Hobbies and More - Marklin Trix etc
Eight Wheeler Models - Limited edition models of American 19th century locomotives and rolling stock
Falcon Figures - 1/48th Scale Figures
Fine Art Models
Foothill Model Works
Grandt Line Products, Inc. - Required parts for scratchbuilders!
Great Decals!
Hattons - UK store, mostly 00 standard gauge
Karat Creek Model Design
Miniatures by Eric
Model Trains International
Morgan Hill Models - On30 models, very nice!
O Scale resources
Oso Publishing Company & Evergreen Hill Designs
Pepper 7 - Online store with great pictures!
Precision Scale Co., Inc.
Roundbell Hobby Products
Scale Hardware - Small fittings and bolts.
Walsall Model Industries - British loco drivers in O, etc
Westport Model Works
Wright Trak - HO modern models

Prototype information

American Memory - Awesome collection of photos and plans
British Columbia Archives - includes railroad sources
Colorado Railroad Museum - Golden, Colorado
East Broad Top Railroad Historic Roster
Fallen Flag Railroad Photos
Friends of the Tanana Valley Railroad
Industrial Archaeology - Many photos of oddball places and links
Industrial Railroad Locomotives - NE Rails
Industrial Narrow Gauge Railways
(late) 19th Century Railroad Resources
my Espee Modelers Home Page
Narrow Gauge From Off The Beaten Path
National Railway Historical Society (NRHS)
NOAA Photo Library - Historic National Marine Fisheries Album
Northern California Railroad Pictures
NorthWest RailPics Freight Car Archives
Pacific Coast Narrow Gauge - great reference site!
Peter J. McClosky's Southern Pacific Railroad Web Resources Page
Railroad Extra - online book and paper/CD books
Rob's Pennsylvania RR info - great reference including earlier cars
Ron Knepp's photostream - Small Baldwins and nice model shots
Roots of Motive Power - Willits, CA
Sandy River & Rangeley Lakes Railroad
Shay Locomotives Reference
SLIM RAILS - Links to the Narrow Side
TrainWeb - Rail Travel, Transit - Model Railroading - Garden Railroads - Amtrack Railroads  & Railroading
Unofficial Home Page of the Toledo and Ohio Central Railroad
Welcome to Mid-Continent Railway and Museum
Western Trails Project - Photographs - Kansas State Historical Society White Mountain History
Wisconsin Logging Railroads
WW&F Railway Museum

Publications and Web Groups

Model Railroading magazine index - still in beta? Lots of data though...
Narrow Gauge & Shortline Gazette - A Magazine For Model Railroaders
O scale trains - modeling for the O scale craftsman.
Steam In The Garden Online
TrainBoard.com - message boards

Reference and Standards Groups

British 1:87 Scale Society
Information Train Station Railroad Links Directory
Light Railway Research Society of Australia Inc
NMRA - Pacific Coast Region - I am currently a member
North American Steam Locomotives
NTRAK Modular Railroading Society, Inc.
Rails USA - All Rail All American Search Engine and Directory
Railway Technical - Modern railroad reference
The Scalefour Society