What are some good online retailers to buy audio/video cables from?
HDMI, DVI, Coax cables, etc...
Ebay, Ram, and Crutchfield are some I've checked out.
Monoprice.com
Bluejeanscable.com
spring to mind.
I second Ken's advice, have purchased most of my cables from Monoprice or BlueJeans Cable. However, my 12 gauge speaker wire I found on Ebay in a large spool.
I bought my 12 guage from Bluejeans cable (perfect if you are doing in-wall installation, the best price on the internet for CL2 rated wire).
Got all my video cables from monoprice, much cheaper than bluejeans.
Ethan, ditto on MonoPrice; no need to pay more.
Signalcable and CobaltCable. A little more expensive, but justified. Not the "snake oil" stuff.
Monoprice
TotalSignal
BlueJeans
The BJC stuff is more expensive than Monoprice or TotalSignal, but I do think it is worth it depending on your needs. The custom length cables from BJC are truly high quality, and their service is fantastic.
My first setup with my Axiom gear used Blue Jeans Cable. AWESOME quality, and a good price (compared to rip off brands like Monster) for what you get.
In my latest install of my gear, I had to leave the premium BJC stuff in the walls, and I didn't want to drop hundreds of dollars into cables again. So this time around, I went with MonoPrice cables. I picked some of their better cables and they look to be *almost* as good as BJC (BJC had better connecters, at least when I got them) but cost about 1/4 the price. I have been very happy with them.
partsexpress and pccables.com also have good prices.
Monoprice seems to have the best prices and good quality products but the last 2 cables I needed they didn't have in stock