Here are a few, luckily the Good Guys list is much longer than the Bad Guys one.
Good: Knifecenter
Cutlery Shoppe (best prices for Spydercos)
GPKnives
KnifeWorks (often the best prices for Benchmades)
TSA Knives (ghbud on eBay, best prices on Bark River knives)
BladeHQ
Horizon Outdoors (also called NICNAC)
The Knife Tree
Aeromedix (for the Doug Ritter Grips)
Knivesshipfree (expensive but unique choice for Bark River knives)
REI
Bad : Countryknives (too expensive)
Spydieguys on eBay (never bought from them because they never answered my questions)
Working Person's (do not be fooled by what is listed on their site, most of the items are unavailable)
Cheaper than Dirt
In a league of their own: The Blade Shop and their affiliates (Taclighting, Tactical Gun Armory): they will take your money upfront for items they do not have and make you sweat for a couple of months for a refund (if any), seldom answer e-mails and their phone lines are always conveniently busy!