My choice would be:
CPU: Intel® Core™2 Quad Processor Q8200
Roughly the cost can be up to 294 pounds.
So it all depends on each individual requirements'.
I have used the board DQ45CB, it has good features like virtualisation support, amt support, onboard graphics, raid support.
I would advise you to do your own research before getting something.
Check the Intel Desktop Website
All the best,