Before the sequel comes out this Friday here's the original Gears of War for a pretty bargainous price. Obviously a large percentage of 360 owners will have already played this but, for the rest, I haven't seen it this cheap before. I just started playing it yesterday and it's pretty good.
Use code B4U for 2% (~16p WOO!) off.
Not sure if that code still works but it's still on here so I'll stick it on.
edit: Also, cashback available from CashbackKings.or TopCashBack @ 4%. Thanks to AMO1980 for the info.