A Noctua NHD15 is still more than capable of cooling pretty much any CPU out there, especially AMD, and especially especially the new 9000 series which apparently run surprisingly cool. Other air cooling options are available. People also like the Thermalright Peerless Assassin, Deep Cool Assassin 3 or Sycthe Fuma all of which are cheaper. Noise wise, they'll probably be fine in a case sat on the floor.
Short answer: I wouldn't worry about air cooling a CPU unless your going to do some kind of mad overclocking or breaking benchmark records or something.