I'm looking to pick up PGR4 on the 360 for cheaper than chips. (from a reputable website of course...;-) )
Best I have seen so far is Game.co.uk with Quidco for £36. If anyone knows of other websites with quidco or a voucher code currently floating around, I'd love to hear it.
(Note: the two GAME codes on this site are both expired now)