Updated 22.04.2014

Here are some links.

Märklin:
Märklin "mother company" in Germany
Märklin around the world
Märklin product database,  from 2000

Märklin shops in Norway:
Amundsen Hobby, Oslo
Hobbytrain, Drammen
Lokstallen Hobby, Narvik

Very useful information about Märklin:
Märklin user's net
The Märklin Cave

Full size trains:
Voss Now, with a lot of wonderful train photos from Norway
Flåmsbana, the third most visited tourist attraction in Norway
Rhätische Bahn in Switzerland

Other interesting sites:
A Dane in Spain
Dale, an American
Ross' Australian site
Ron from USA
Marklinfan, an Italian site with a lot of wonderful photos
Macfire, a New Zealand site
Osterthun, a site dedicated to German railway
The Auckland Märklin Club
Piet's model railway site
A Märklin site by Hüttel

More links will be added (or removed) from time to time.