This should meet your son's needs well. (It's got excellent reviews and a response time which is just as low as my previous suggestion): Amazon.co.uk User Recommendation
How big is your budget. The 27" HP ZR2740w monitor is widely praised on review sites (where it often gets the award of 'best gaming monitor') but it's not cheap. (£613 on EBuyer).
wow, that sounds good, but I was looking for something closer to £200 it's for my son & I know very little about monitors or gaming or technology come to that!
This should meet your son's needs well. (It's got excellent reviews and a response time which is just as low as my previous suggestion):
Amazon.co.uk User Recommendation