Processors: Athlon X2 4200+ - A beefy dual core chip for just £250.
Motherboards: Abit Fatal1ty AN8-SLI - An expensive but utterly top notch board. £125 including VAT, but worth it for a high end system.
Gigabyte GA-K8N-SLI - A socket 939 nForce SLI board with PCI Express, 3GB SATA, etc. and all for under £60.
I also suggest a "Coolers" section under which the Zalman CNPS9500 has to go. I've had mine for a month and it's amazing. Virtually silent and barely even lukewarm to touch. And that's with an overclocked CPU as well.
EDITED: 1 Feb 2006 20:00 by DAVE!!