Not your normal replacement clone cases; these make your Xbox 360 look completely different.
Firstly the very swish looking case from Zoozen: the Ovo360.
And there's also news of a case from PC case manufacturer Lian-Li. This one's a bit of a beast, but I can't see it overheating.
EDIT: Lian-Li have the PC-XB01 case on their site. Check the Specifications section for lots more pictures. There's one picture that looks very silver to me, so I'm sure there'll be a silver version of the case too.