Some excellent titles now in this range including:
Kameo (I really enjoyed this)
Splinter Cell Double Agent
Maybe even more, it depends what's in your store. These are also for 360 but there's plenty cheap on the PS3 too, including Assassin's Creed. I've been assured that Assassin's Creed is this price countrywide so get them to check it if it's more. Also if the box is grotty or damaged most are happy to swap it for a new one (no trying to pass it off a new for xmas though!). I've heard mention of vouchers in catalogues too?