Ninjalane has just posted a review of some silent fans from Noctua.
A quote from the article:
Noctua Case Fan Review
Many casemodders and enthusiasts are quick to overlook fan performance in favor of what happens to be freely available and why not? A fan is a fan right? Noctua doesn't feel this is the case and has come up with a line of super silent fans that even your cat can ppreciate.
Noctua Case Fan Review