I think XIGMATEK and Scythe make good fans, the XIGMATEK 120mm pushes 72 CFM at 20 dbA. There are others, but these are under $10 or £5. You can spend 20 bucks on a case fan like noctua, but XIGMATEK and Scythe are cheap, silent, strong, and high quality.
Hell, the Scythe "ULTRA KAZE" pushes out 133 CFM at 45 dbA, and if you lower it to about 110 CFM you'll get about 28~30 dbA.
Scythe is known for excellent fans, and XIGMATEK is known for excellent PSU's, Fans, and much more.