I need two lists of the ten best model train related websites, one for
each of two categories. First is the ten best reference sites, with
freely available information about building model railways,
maintaining them, how to choose the right components, sample layouts,
etc.

The second is the ten best websites for buying model train equipment.
These should be based not only on good prices but on good selection
and a good customer service record.

I would like the lists to contain the website name, URL and a brief
description of each one.

Have you picked up a copy of Model Railroader lately? This would be a
good place to start.It has a website, though it's not everything.

Model Railroader Magazine 
http://www.trains.com/maghomepage/maghomepage.asp?idMagazine=3