EVGA CLC 240 Liquid Cooler Replacement Fans
EVGA CLC 240 Liquid Cooler Replacement Fans
Noiseblocker E-Loop
EK Vardar
Bitfenix Spectre Pro's
Pressure-optimized fans from Noctua
If you're unsure, consider checking fans with high static pressure. Static pressure aids air flow through radiator fin stacks. Also, explore PWM fans.
The stock enthusiasts are usually fine as long as you don't force them to run at their highest speed, because they spin extremely quickly compared to most other competitors' fans. Lutfij provided excellent suggestions. I currently own Vardars on my FD Celsius S24, and they perform very well in reducing noise.