SilentPCReview is a great souce of information for this, as they look at both voltage regulation ability, efficiency and noise levels.
PCs need 3.3, 5 and 12 volt sources of power for the different components, so for any practical implementation, you will still be constrained to a SMPS. You might be able to hook up your USB output or sound card to a cleaner (linear) power supply, however.
Fanless power supplies sound like a great idea... but you need to be really sure that your system will run cool enough to make this work. Heat kills electronics in a hurry. The best fan equipped SMPS solutions are extremely quiet at typical power loadings (20-22 dB in free air typcially) and have a temperature controlled fan. As a result, these power supplies will be quieter than any but the quietest 2.5in laptop hard drives, especially when placed inside a good case and supplying typical loads.
Based on what I've read at SilentPCReview and elsewhere, I'd go with the Seasonic S12-500 or S12-600 if you want to build a relatively future-proof (dual PCIe power connectors), general purpose (more power than currently needed) system.
If you are building a dedicated media PC with lower power requirements and don't need PCIe power connectors, you can look at some of the lower power supplies, like the Seasonic S12-300 or 430, Seasonic SS-430HT 80+, Antec Neo HE430, etc.. (There is one more from another company that I can't remember at the moment - sorry.) Going with a bigger supply usually has the advantage of allowing higher output before the fan ramps up in speed (and thus noise). The penalty is that they aren't as efficient at lower power levels. I haven't looked at fanless supplies, but those are an option as well if you are confident in your system cooling and power requirements.
Hope that helps!
