I'll be adding links on this page for dealers and auction houses I have had good experiences with, and some informational sites. Contact me if you would like to have your site added.

Note that both NGC and PCGS have registry programs where you can list your coins and display images. Actually not a bad idea to keep images off site of your collection. Personally I use the NGC registry, PCGS will only accept PCGS graded coins while NGC accepts both. I don't see limiting myself to only buying PCGS. Both NGC and PCGS also have forums to join and interact with other collectors.

NGC - One of the top two TPG's
PCGS - One of the top two TPG's

ANA - American Numismatic Organization, well worth joining.

Information Sites

Coins GB - good collectors site and forum.
Coin Imaging - A site by Mark Goodman with several good articles on photography. His book on photography is well worth the price, even though my skills suck, they are much improved since reading this volume.
Gems by Glenn - A collectors site with many good coin images, also some very interesting mineral and rock photos.
Wildwinds - An excellent site for information on ancient coins and values.

Dealers & Auctioneers

Northeast Numismatics - Well known dealers with some exceptional U.S. and world inventory. Many of my British and German pieces come from NEN. Number 1 in my view for World coin dealers in the US.
RCToners - A top notch photographer, and usually a good assortment of Early Commemoratives as well as other US coins.
Goldberg Auctions - One of the top auction houses in the US for World coins.
R.P. Coins - UK dealer with a very wide selection, Rob is very knowledgable on early copper in particular, one of the few dealers I buy raw coins from.
Colin Cooke - Another well known UK based dealer, another of the few I buy raw coins from. Good images and honest descriptions when you call or email them.
David Lawrence Rare Coins - Well known dealer and auction house, I've bought quite a lot of early US Commems from them.
James Hanna - Affiliated with Northwest Coins, very pleasant to deal with, attractive coins with good prices. I've picked up some nice German material from Jim as well as the MS67 French Franc.
Heritage - About the largest auction house for coins, also art and collectibles auctions.
The Copper Corner - Dealer in copper coins, very informative site with info on a lot of the pieces he bought from the Boulton collection.
Jonathan Kern - Respected dealer in ancient and world coins.
Aspen Park Rare Coins - Well known dealer with a very nice inventory of world coins.
Jetproofs - Often has a very nice selection of early commemoratives.
Classical Numismatic Group - World and ancients, both inventory and regular auctions, these are the guys that got me started in British coins, very good to deal with.
Karl Stephens - Dealer in world coins and medals, I have not bought anything here yet but he has some very interesting pieces.
Ancient Silver Coins - Information on ancient coins and pieces for sale on ebay.