AMD Build
Samsung 1TB Harddrive £73.56
Asus 4850 £118.06
ASUS M2N68 nForce 630a Socket AM2+ £51.20
Phenom 940 II x4 £237.03
Corsair 4GB (2x2GB) DDR2 1066MHz £91.23
Total £571.08 inc vat
Intel Build
Samsung 1TB Harddrive £73.56
Asus 4850 £118.06
Gigabyte GA-EX58-DS4 iX58 Socket 1366 (cheapest mobo I can find) £197.02
Intel 940 £474.69 (cheapest i7 I could find)
Corsair 4GB (2x2GB) DDR3 1333MHz (cheapest DDR3 I can find) £102.26
Total £965.59 inc vat
The Phenom II build is 394.51 cheaper than the i7 build
All components from: Ebuyer.com
Edit:
We know Phenom II is cheaper, i still think Core i7 is more future proof.
Just re-iterating for the few people that still say the pricing variations between the PII and i7 as being small, also giving a UK perspective on builds.