why spend a fortune?...most of the stuff people recommend is bullshlt..
i've built a couple systems using a thermaltake volcano III ($12 CDN) and it's literally almost DEAD silent, including a generic PSU fan running.
another good one is the thermalright CB-6L, which i've also used, but it's not as cheap, nor as quiet..close tho. (and cools better)...
for anythign under 1.4 GHz, the volcano III is one of the quietest/cheapest solutions...plus it uses the same sink as the volcano 5..just slap on a better 60mm in the future if u want better cooling..the fans run at ~4000rpm.