There are many people and companies out there with a lot of good information about Märklin model railway.

Updated 22.04.2014

Here are some links.

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.