fractal design Node 304 is my favourite looking mini itx for quite cheap. There's also the bitfenix Prodigy which a lot of people like, but it's expensive and quite large for a mITX.
i was debating between the fractal node304 and the corsair 250D. i went with the evga hadron air. its really nice. dont let the price put you off -- its got a built in 500w gold rated power supply built in, hence the price. awesome little case.
EDIT: its also significantly smaller than other m-itx cases like the 250D or the bitfenix prodigy, though this does limit some of the things you can put in there (h100i will not fit without modding the case, for instance)