I personally use, and recommend, these vendors:
- Deep6 for the things they make: regs, fins, used to make wetsuits. I haven't tried the computers but I understand that they are good.
www.deep6gear.com
- MAKO for the things they make: weight belts, lead pinch weights, masks, snorkels. I haven't tried the wetsuits or the dive flags, but they're both supposed to be good.
www.makospearguns.com
- SeaSkin for drysuits, and drysuit accessories like drygloves, undergarments, P-valves, etc. They make high quality custom drysuits at a great price point.
www.seaskin.co.uk
- DGX for just about everything else: BP/Ws, lights, computers boltsnaps, reels, STAs, DSMBs, tanks, cutting tools, parts, hoses, SPGs, compasses... honestly, you name it, they've probably got it at a good price. They also make a lot of their own stuff. Customer service is excellent, free shipping for orders over $100.
www.divegearexpress.com