These comments are for decent quality production knives only.
As a knifenut on a budget, I really shop around, but I prefer to stay local with as many purchases as I can. You may not be able to use the cheapest and most reliable places I've found. Both AMH & TSC are local, and I only see them at Gun & Knife shows.
AMH Cutlery - Hoag & his son are among the best. They have hidden treasures which you may not find elsewhere.
Total Sharp Cutlery Company - Mike & Tammy have been very good about price breaks for regular customers. Totally reliable.
MJ&S Knives - Mark is really great about giving the customer what he wants at a reduced price. He's easy to find on the web and very responsive to email.
Ultimate Outdoors - Cliff Hanks carries a limited selection, but some of his prices are really good. I found a Civilian there at a rock bottom price last year.
I know there are a lot of other really great dealers who can be both cheap and reliable. Because my budget is pretty limited, I have not been able to order from many of the fine dealers you can find in the BladeForums links.
I almost didn't post to this question because I didn't want to leave out some of the really good dealers just because I haven't ordered from them. You should check The Good, The Bad, The Ugly! forum and search through those posts. There are a lot of good comments in there.