I wouldn't recommend it if you want to build a rig capable of maxing out Battlefield 3 , but for anything less Lian-Li has just announced an elegantly sized and extremely good looking case, the PC-TU200 .
Standing just 32cm high by 21cm wide, its luggage-like looks are set off by a large handle on the top. Obvious uses are for a system you plan on hauling around to LAN parties, although it's one with awesome modding potential if you're that way inclined too.
The thing is, with modern components running so cool and quiet, it's getting harder and harder to justify the giant towers of the past for gaming. The PC-TU200 may be designed to fit a Micro-ITX motherboard, but that doesn't mean a computer full of compromise. I was eyeing up Zotac's Z68ITX-A-E just the other day – that's a tiny mobo that'll take the latest Core i7 processors, if you'll let it.
That may not leave you a lot of options for expansion (it only has one PCI-E port) but if you're aren't planning on going for SLI or Crossfire graphics, it should have all you need. The PC-TU200 has plenty of space inside for four hard drives and a full length 300mm graphics card, which should be enough to squeeze in an HD6950 or HD6970 if you try.
I should mention that I'm a big fan of Lian-Li's cases. While I haven't seen the PC-TU200 yet – and will hold off making a final judgement about packing a high end GPU and CPU in there together until I do – if it's any where near as well engineered as the majority of their product range to date then there's a good chance I'll be rebuilding my media centre machine again.