Silent CPU Cooler?

There are NO silent cpu coolers.
Quiet perhaps, but not silent.
Any sort of fan will make some noise. 700 rpm is largely inaudible. Up to 1000 rom it will be quiet.
Larger fans push more air at lower rpm, so that is what to look for.
I might start with noctua or Phanteks.
Here are two:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835608041
http://www.newegg.com/Product/Product.aspx?Item=N82E16835709011
 
Solution
What are you putting this into/onto? What programs do you use? Is this for gaming? Productivity? What CPU are you putting this onto? Are you overclocking?

Most air coolers will get the job done very well. Depending on your enclosure and processor workload, I would recommend Noctua, Gelid, Scythe and pretty much any other high-end CPU cooler/fan manufacturer. If you can provide more specifics such as listed above, I can give a better recommendation.