Hi

I want to build Fanless PC - minimum performance in order to get minimum TDP:
CPU: Athlon II x3 440
CPU Cooling: SCYTHE Ninja 2 Rev. B SCNJ-2100 - fanless
MD: GA-MA78LMT-US2H
Memory: KINGSTON 2048MB DDR3 1333MHZ
HD: WD CAVIAR GREEN 500GB 32MB SATA2 7200 RPM - WD5000AADS
Power Supply: FSP ZEN 80Plus 400W

Which ventilated fanless case is recommend?

I'd recommend at least one fan. And the HDD will be a major source of noise and will overshadow any decent 600rpm 120mm fan. So I suggest you look more into silencing the HDD before looking into fanless case designa.

IMO the entire fanless concept is a moot point, as long as you use good fans. You're opting for a sub-par PC, when you can have betters specs at the same cost and better reliability. I sleep with my head 2 m from the PC in my spec list and it's dead silent from that distance.

Sorry, that was my rant for today!

Will be plainly audible when everything else is silent.

You could either replace it with a SSD if you want silence, or keep the hard drive and install a few ultra-quiet fans in the rig (since the hard drive will be louder than the fans anyway).

Can you offer me more silent HDD?

In this case I should take noise-absorbent case.
I was thinking to buy Antec Solo and replace the original fan to NOCTUA NF-S12B-FLX 120mm, is the better case in this budget?

An SSD will be completely silent. But WD GP HDDs are pretty good. Also do consider a 2.5" laptop HDD, they're generally more quiet. Remember to soft mount the harddrives, though!

About any case is good enough for your build, as long as it has 120mm fans! So go for one you like.

In particular, my favourite hard drives are the WD Scorpio 5400 rpm, and Intel X25 SSD. Depends what capacity you need of course.

I can agree with the others re: the fan. I was going to go fanless myself, but the low-rpm 140mm fan on my Scythe Orochi is so quiet that it is simply inaudible from a reasonable distance, even with a low noise floor. That, and it reduces temperatures substantially.

Those are my favs too!