Medal of Honor (Honour;)) for the PS3.
Also available at The Hut for £17.93.
If you've got the Xbox 360 (which is far superior!) you should check out the ASDA Entertainment deal http://www.hotukdeals.com/deals/medal-of-honor-xbox-360-17-91-8-qui/829803
where the price is too £17.91 and you have the chance for Quidco.
Not much else to say, other than this is the cheapest I can find at the minute. Just a heads up really, don't expect too much heat seeing as the saving is pretty pathetic (2 pence!)