Lynn, I have had very good luck with Caboose Hobbies out of Colorado.They have an excellent inventory.
Scale model supplies in St paul when you shop locally is about as good as it gets in the cities
For DCC I use Loys Toys talk to Fred Standish, he's very knowledgable.
For n scale specifically try
4nscalesupply
Standard Hobby supply has been pretty good with me.I recently purchased an On30 BLW C-16 on a special coupon(about 1/2 price) No problems and very timely.
others I have listed
N scale supply
discount trains online
Any google search will bring up a ton of options.
Find one that suits you by checking out thier sites usability and inventory.
Caboose Hobbies i have found to be a top inventoried shop with excellant service including follow up to insure your satisfaction.
They beat Duluths shop hands down in every category from friendliness to price from availabilty to complete performance.
They are the real deal and get the bulk of my online hobby shop purchases.In fact, they get far more than my LHS (70 miles away). Why, because they are simply the best ive found!!
Todd