RAM: I would personally go with the G.Skill Ripjaws Series 8GB (2x4GB) RAM. I would suggest the Corsair Vengeance, but the heat sink clearance will become an issue with those (unless you find a slim heat sink version).
GPU: Depends what your looking for as far as gaming (Ultra High settings I assume). If budget is no problem, I would run a single MSI Lightning Xtreme GTX 580. You could also SLI 2x GTX 570s for around the same price and get more power out of your rig. If budget becomes an issue, then I'd look at the ASUS Radeon HD 6970. .
SSD: £160 120GB Intel 320 Series - You need not buy this now 'coz your board already has 20GB SSD built in, but that will barely hold Windows with all it's updates, page files, hibernate files and what not.