I used to have a Shuttle (AMD XP 2000 era) in the living room as my MythTV frontend. I got it second hand as a customer-returned unit at Aria computers in Manchester. It came with the ordinary PSU so I did a little switcheroo at work where we had a Shuttle with a SilentX PSU that lived in a machine room, despite it being an Intel box the supplies swapped over without any issues.

It PXE booted so had no discs in it and had a passively cooled gfx card. Once the big fan had ramped down after boot it was really quiet, certainly not obtrusive.