I've discovered that I have a horrible weakness for the metal cases that some of the cooler "collectors editions" of the games come in.
I can resist the 'bonus makeing of DVD' or mini-strategy guide or 'metal figure' that comes in most collectors editions. But the metal cases get me every time.
I don't know why, but I find them REALLY cool. I love my Halo 2 case, and I know I'll be unable to resist the Gears of War CE metal case.
Damn you clever marketing people...