HMV are currently running a promotion where you get Need for Speed: Pro Street and Halo 3 free when you buy an Xbox 360 pro console.
I bought one today in Edinburgh and asked if I could switch the games and was told that was no problem. I got Mass Effect and Ace Combat 6 instead of the 2 bundled games.
The only games I couldn't get were Guitar Hero 3 with the wireless guitar and the special editions of COD 4 and Mass Effect.
HMV are usually pretty good on being flexible on their deals so you shouldn't have any problems getting this deal at other stores.
It says in store that the deal is only for 1 week but I don't know when the week started, so get down there quickly!