AC4L has been around over 10 years and heavily promoted and recommended on AVS forum as one of the premier authorized refurb resellers. They're also located just down the street from me and I have met the owner and toured their warehouse. Order with confidence as well as a 1 year warranty on Denon AVRs.
Call around to places like Electronics-Expo.com and jr.com to see if they have any new 4311's left. With the new 4520CI coming out they may deal on the outgoing 4311. It's been $1250 before and the new one comes with a 3 year warranty.
Hello Chris-to expand on the internet, Denon authorized, dealers: go to the Denon website and you will find al full list under "where to buy-a simple phone call to their 800 numbers, and asking sales for their lowest price, should give some satisfactory results.