I've just upgraded by motherboard and processor and I'm looking to upgrade my graphics cards too, but I only have around £250 available. Could possibly stretch to £300.
My old (current) graphics cards are 2x Radeon HD5770 (XFire)
My new motherboard is an ASUS Maximus VI Extreme
and the new processor is an i7 4770k
Originally I was going to get something like 2x GTX 480s and a third cheap card for PhysX, but then I discovered I wouldn't be able to run my 3 screens independently (Not a fan of Eyefinity or Surround). I was very surprised by this as my OLD 5770s can handle 3 screens just fine. Running 3 individual screens is a MUST. They're also different resolutions which probably doesn't help (2x 19" 1440x900 + 1x 23" 1960x1080).
I don't mind if it's ATi or NVidia (Although I may be bias towards NVidia - I like the idea of running a separate PhysX card) and I'm in the UK so it's got to be available here.