Ok, I know there are a lot of Apple haters out there, but I have been teetering on the edge of ordering one of these retina screened 27" iMacs since they first came out. This deal finally made me jump, here we have the newest release of the top spec (without any extras), so this is a quad core i5 3.3Ghz with 8GB RAM and a 2TB fusion drive. Also comes with the new Magic Mouse 2 and the new Magic Keyboard.
While 8GB of memory is a little light for a computer of this type, Apple are notorious for charging too much for memory... A quick search of the internet found a 32GB upgrade for £123 including shipping.
Seeing as the Apple Store price for this spec is £1849, a saving of £269 on a machine which has only just been released seems pretty hot to me, and as the seller uses Paypal, you have buyers protection from Ebay.
I know this won't be for everyone, but if you are looking for one of these, I have never seen cheaper!
New link same price same dealer here http://www.ebay.co.uk/itm/New-Mk482B-A-Apple-iMac-Retina-5K-27-inch-3-3Ghz-i5-Quad-Core-8GB-2TB-Hybrid-UK-/121808366275?hash=item1c5c582ac3:i:121808366275