I'd have to say the MGS4 steelbook that came with the Japanese CE is my fave but I am a MGS fanboy. Lovely matt/brushed metal finish.
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Mirror's edge is the one I want most (love that game) but I'll never get one, no way I'm paying that kind of price for it.
I'm coveting the PoP forgotten sands steelbook as well at the moment, might hev to get me a PS3 copy of that.