SPCR

I saw this reviewed on Tom's Hardware. They put a watercooler in it, but given that it features "large ventilation holes on all six sides", it occurred to me that it might be suitable for a completely fanless build.

I am not sure how that case would work for a passive case - the small holes will let a little air flow, but without fans, it will be minimal. They put filters on the bottom opening - but dust will get in where ever air gets in.