I upgraded an AM2 system to a dual core AM3 Phenon II CPU, which came with what looked like a decent cooler in the retail pack. But when running anything that uses the CPU much the cooler fan revs up to high speed and is extremely loud. Even Firefox will make it spin the fan as much as Kerbal Space Program does. (When it's hard to tell the difference between the sound effects in KSP and the CPU fan noise...)

I'm planning on moving this CPU to an AM3 board and unlocking it to quad core so it will need even more cooling. I have an AM2 dual core CPU that will work in this system but it runs hotter than the Phenom II. With the cooler that came with the AM3 CPU the AM2 chip has it running full speed as soon as Windows starts to boot.

What's available that will keep the CPUs cool and quiet?

Perfectly quiet? Liquid cooling.

If it is a fan-based cooler make sure you get one with 120 mm fans and not 92mm or 80mm. In general the larger the fan the more air it moves but at lower RPM.

try the Thermalright Macho:

http://www.thermalright.com/html/products/cpu_cooler/hr-02_macho_reva.html

Or if you are on a budget, the Coolermaster 212 EVO is a good one, retailing at 35USD, but for these coolers you need to have a wide enough case, just make sure it fits before you order. There are also nice coolers with 2x 92mm fans for about 5USD less.

The Thermalright Macho retails around 53USD.

... and watercooler kits are noisy as well, not the fan on it but the darn small pumps that make some real noise... Sure you could fork out some serious cash and make a low noise custom watercooling system...