FSP Group's fanless Zen 300W PSU did well in our goliath of a PSU roundup, but it was slightly underpowered and underconnected for some (not in terms of absolute output power but in terms of what's available on individual rails).
The product of a different design team to the one that created the original 300W unit, the new 400W Zen is reckoned to offer the same silence as before but with a slightly improved connector bundle and that higher output. It'll be a bit more expensive than the older model, and the good looking mesh of the 300W version is now gone, but it should still rate well under scrutiny.
If you want to pick one up, look for FSP400-60TNF. Pics follow.