I've had a lot of success in my rig with Noctua's fans and Scythe's S-Flex series. Admittedly they are probably over-priced and there are better for the money, but heck, they sure are quiet.
*Forgot to mention the Scythes are on newegg in the 120mm fan category and the Noctua's are too, I got mine however at theheatsinkfactory.com*