Following that overwhelming response :)
If anyone else is asking the same question, I went for a Sony VAIO F12, with an i7 740, 8gb of RAM, an Nvida 330M graphics card and a 500gb hard drive. I even got a free blu-ray writter!
I'm delighted with it and would recommend it (though the F13 is now out with USB 3.0 and next month we should see the F14 with a 3D display.
But this is a brilliant computer, and for the spec, a very competitive price.