personal favourite cos its fantastic value for money (high end psu for mid range price)
OCZ 600SXS StealthXStream 600W PSU (3 year Direct Manufacturer's PowerSwap warranty) - OCZ600SXS - microdirect.co.uk
dont ever skimp on a psu, power wise and price wise. a cheap psu is mor elikely to blow on you and take half your rig out. power - its always better to get more than you need, your better off when your psu is only working half its capacity to power your rig, rather than have it work at peak (kills life and then fails!)
also you should have no problems when it comes to upgrading to anything bigger and better