If you want a modular PSU then these are good options:
Adata HM 650W 80Plus Bronze Modular £70http://www.ebuyer.com/261364-adata-hm-series-650w-80-plus-bronze-psu-8x-sata-2x-ahm650bzceu
Antec Truepower New TPN-650 80Plus Bronze Modular £65http://www.scan.co.uk/products/650w-psu-antec-truepower-new-modular-82eff-80-plus-bronze-sli-crossfire-eps-12v-quiet-fan-atx
Personally I would happy running a build with two 6850s on a 550W PSU, but for some reason that is not the case for most people.
Asus P8Z68-V £124http://www.scan.co.uk/products/asus-p8z68-v-intel-z68-s-1155-ddr3-sata-iii-6gb-s-raid-sata-pcie-20-(x16)-vga-on-board-atx
If you will be overclocking then I think you will at least want to give yourself the option of installing an aftermarket CPU cooler, in which case it would be wise to go for RAM without tall heatspreaders (which are unnecessary). There are Corsair Vengeance Low Profile sets for instance.