Play around with the base spec configs - more HD and ram options.
For example, you can get the 2.0GHz 320GB model with 2GB ram, but for another £10 you could get 2.26 model with 2GB ram with 120GB. (£659)
My choice is going to be 2.26, 250GB, 4GB RAM. Comes out at £819 rather than speccing the 320GB model with similar RAM and processor options for £850. I'll take the £30 saving over an extra 70GB, this thing is expensive enough already 😀