FORUMS (English)
JNS Forum The Japanese Modeling and Japan railway enthusiasts forum! In english with lot's of great information beyond just Japan.
N A very deep forum covering a good variety of topics for 1:160
N  Another deep forum, focusing on North American trains in 1:160
N Gauge Forum A new forum based in the UK based on everyone's favorite gauge!
Railways of Germany  An English forum with a focus on German railways in all scales.
Yahoo Kato Unitrack Group  A repository and forum (sort of) for all things Kato Unitrack.  Very useful!
Model Rail Forum Forum with a focus on the UK, but also some Continental and North American.
Trainboard - A high traffic forum, although only one 'section' just for N Scale (this links to it directly) primarily US/North American, although a few 'global' modelers make it online occasionally
Skyscraper City Forum all about the various facets of skyscrapers A really great presentation of the locomotives and rolling stock across Europe.  Fun to browse to check out the various locomotives from the many diverse regions of Europe

FORUMS (Non-English)
Spur-N-Schweiz  A Swiss forum for N Scale (German)
Le Forum du N A French forum for N Scale (French)
N Spoor Forum A forum from the Netherlands (Dutch)
Benelux Spoor Net Primarily Dutch forum covering the 'low countries' in all scales. (Dutch)

(shops and dealers I frequently order from with good results!)
Plaza Japan on eBay.  A merchant I've happily used many times for those hard to get items from Japan (or to get a better price!)
Eurorailhobbies Canadian-based importer of all important European brands, generally has the best prices and always good service.
DM-Toys an online retailer specializing in N Scale...lot's of European cars/buses and other details that are hard to find elsewhere
Reynaulds  US importer of all important European brands, great service as well.
DCC Train  Conversions to DCC
HobbySearch Japan Another good source in Japan for hard to get items!
Transmondia Which I had the great pleasure of visiting in person!
Trains 160 France-based retailer focusing on N Scale! Yeah!
Gaugemaster UK another shop I had the pleasure to visit!
Modellbahn-shop Lippe German based retailer with a nice site (in English and other languages) 
Modellbahn Kramm Another German retailer with an English language site capability 
Comboios Electricos An online retailer from Portugal, features a great selection of some of the more difficult to find Spanish brands as well as the more traditional German ones!  Some parts are in English, but most is in Portuguese.
TrainAidsA has some really useful, 'beginner friendly' LED lighting supplies.
Evan Designs has LED kits that really make it easy for the LED beginner.  I still get some of their flashing LED's and have a few of their pre-wired (i.e. resistors and stuff already prepared) LED's for quick installs.

N Scale Limited Great modeling information online magazine
The DCC Wiki A ton of information all about DCC.  A good place to go for education or help!
Spurweite-N is a massive database of just about everything ever made in N Scale.  Worth a look, but unfortunately you'll have to brush up on your German (German)
Spookshow's Model Railroading Encyclopedia is a great treasure trove of US N Scale history, with a similar database of US N Gauge production to the above.
1zu160 A German language site covering all the new releases in N Scale...some of the news is here first before its anywhere else in any language! (Germand)
Plans en Modélisme Ferroviaire A French site with over 35 N Scale track plans (French)
MODELISME FERROVIAIRE A l'Echelle N is another French site with a comprehensive overview of French models in N Scale (warning: annoying pop-ups!).
Modeltreinen Database - a Dutch site that apparantly has all of the content from the now defunct "" - which was a great Dutch site with images of manuals from many out of production locomotives from many European manufacturers.
Yahoo Japan Auctions N Scale Auctions site on Yahoo! Japan.  All in Japanese, and difficult to impossible to order if you're not in Japan, although there are agents who can bid for you.
Mobablog Massive site covering German model railroading (and more) (German)
Alte Modellbahnen - (German) This Forum has a category on 'old buildings ("Gebaude" in German) if your interested in that niche area of the hobby!  

Turnout Indicator Circuit help
Guide to Circuit Symbols

DCC Help
NMRA DCC Decoders overview