Noctua is a small Austrian company specializing in high end computer cooling. As the successor to the highly regarded NF-S12, the B variant has a few refinements including a new beveled fan blade tip design. With the ability to change the RPM via a "low noise" adapter (which appears to be just a resistor), it promises to be very quiet as well.
As you can see in the image, the fan blade is quite unique in design. It allows for 10% more static pressure and airflow than the predecessor. With my SPL measurement device, I saw only 19dB at the highest setting going down all the way to 8dB at the lowest. It was remarkably quiet.
The color scheme is a welcome change from the commonplace black fans and the elaborate but cheesy LED filled clear fans. That, coupled with its high performance with very low noise makes it quite an incredible device. I would definitely recommend this fan for those building a new PC. If only the fan had pulse-width modulation in order to dynamically control its speed, then it would be about perfect.