For those who are wanting the ability to control the fan speed but don't want to have to spend the extra bucks for a Rheo setup, head on over to 2FastCPU. They have posted a review that tells us about the Enermax 80mm x 25mm Adjustable Fan. Is it worthy of our overclocking dollars? here's a snip:

"Though the most special feature of this fan isn't the hip looks, rather the ability to manually adjust the fan's speed. Three speed settings give you complete control of how the fan operates in your computer. There is a 'Low' speed setting which allows the fan to run at 25 CFM / 21 dB. The 'Mid' setting allows the fan to run at 32 CFM / 27 dB. Last but not least, if you need to have the power house (High) setting, it allows the fan to run at 40 CFM / 33 dB. This manual adjust function gives great variety when choosing speeds. One of the three will get the job done."