This is not usually a category of computer that we report on, but MSI has just released a fanless, embedded desktop for industrial applications. Silent PCs seem to be talked about more and more frequently, and I am not sure how much of it is industry trends (as opposed to me just paying more attention). Their focus on this design is performance while remaining rugged and, as mentioned a few times, fanless.
Note that it supports CPUs with a maximum of 35W TDP. This leaves room for MSI to include up to a Core i7-4785T in the device, but we do not know if this is actually offered. It has four expansion bays, one PCIe x16 and three regular PCI slots. It does not have an ISA slot, though. I am sure this will be disappointing to some enterprises, and Josh. He probably still has a graphics card for it. You might think I would be joking. I am, but sadly I also am not.
For power, the device can accept anywhere from 9 to 36V DC. Basically, it seems to be based on laptop components with expansion slots for add-in boards. You can also purchase a fan "module" for it if, for one reason or another, it is still the best PC for the job even if it wasn't fanless.
Pricing and specific availability are not provided, but it is apparently released.