If you need a good seller, scan.co.uk have been pretty good. If you sign up to certain forums (e.g. Hexus) and get 25 post, you can get free postage.
1) I wouldn't go for last generation Q or E Intel processors.
2) As far as I know, very few photoshop actions actually support graphics processing or multi-threads.
My suggestion:
* Core i3-560 (saves you a graphics card) ~£100-110 (the 540 or 530 is another £20 or so cheaper)
* Intel DH55TC ~£60-70
* 2x2GB of DDR3-1333 (=PC3-10600) ~£50
* Samsung or WD 1TB drive ~£40
Depends on how quiet you'd like your computer. The high spindle-speed HD vibrate vigorously, causing the case to resonate. Best option would be an SSD bootdrive and a slower suspended storage drive. I believe Sharkoon produces elastic suspension drives cages, or you could DIY (works a treat).
* Quality power supply, with the lowest wattage you can find. For example Enermax.
* Case: my recommendation is an Antec Solo, but these retail for more than £70 here, but has drive suspension built in. Any case will probably do, but it might be more difficult to keep your components quiet.
* CPU cooler ~£30, for example Scythe Ninja or Mugen. These are very efficient and come with an excellent fan
* Another Scythe Slipstream fan as main exhaust ~£10
* DVD/Bluray
* If you're a student, you can buy Windows 7 (Home or Professional) for about £30.
Alas, Intel has not properly implemented USB3 in their current line-up. The motherboards usually have less feature than equally priced AMD pendants.
For AMD, you could chose a Phenom II X2 555 and for example the Asus M4A88TD-V EVO/USB3 instead.