For my next PC I have already bought an Enermax Pandora case, a Cooler Master 400W PSU with a big silent fan, silent fans for the case and dust filters, I'll make all the fans excepted the PSU's one blow air inside, while all the air will go out through the PSU. Now I want low power consumption components, so a mobo with onboard AMD 780G graphics, fast enough for most games older than 1.5 yrs and so good for all my games till next year, as I'm far behind playing all the games I would like, with it I'll be OK for enough time to wait for a much faster, but economic, silent and low power GPU to be released when I'll want or need to upgrade it. Regarding the CPU, an Athlon 64 X2 4850e should be fast and cool enough, I'll consider a quad core for upgrade when they'll be cheaper and will offer at least 2.6GHz for low end models, so that worst case performances with SW unable to use more than one core won't be slower than those with a current mid range dual core (that's still the best for most unoptimized SW).
Taking into account the components I've already bought I should stay within 400€ (~$620), so even after a graphics card upgrade (next year medium-low end should be faster, cheaper and cooler than current medium-high end) I should stay comfortably within 500€ (~$780).
