StoresGames Workshop Needs no introduction.
Forge World Get your Apoc models here.
Black Library Games Workshop's Book store.
K & J Magnetics, Inc Good place to get magnets of any size.
The War Store Buy 40k stuff at 20% off.
Battle Foam Buy custom foam trays for your cases.
Armorcast Get cinematic effects for your minis and some cool bases.
MiniWarGaming Buy 40k stuff at 10% off.
Micro Scale They sell lots of decals. But the main reason for posting it here is because of their Microset and Microsol products they sell
(here). They are used to make your decals look like they are painted on. I've been using it and have had mixed results, but each time I use it I get better with it.