Here's my take Orangeman (quite a few more knowldegeable folk around here though),
Here are a few, but not all, fan control options:
Fan controller software (freeware) called Speedfan, which, once set up, can automate the whole fan control experience. Eg - you can set different fan speeds at different temperatures. Great piece of s/w, not very user friendly, it means that your fans go at max until windows is loaded and the speedfan kicks in. Only supports certain mobos, and sometimes does not support case fans. I have it driving my CPU fan, which is good, because with a manual system, I might one day forget to turn it up and then.... fizz
Manual ones which range from 5V to 12V: eg the very much favoured Akasa FC03
http://www.overclockers.co.uk/showproduct.php?prodid=OA-002-AK&groupid=701&catid=57&subcat=189
An Akasa Amber or most other decent 120mm fans running at 5V run very quietly.
Manual ones which range just over 0V to 12V: I don't think you can actually switch fans off using these controllers, but you can run the voltage so slow it doesn't start. I've got one, it's called a Sunbeam Rhoebus. Works well, but would not advise to use it on critical devices like CPUs/GPUs.
Automatic fan controllers which allow you to switch off. For example (and this is the only one I know of) the T-Balancer: fairly expensive, takes a lot of setting up, but once done, a lot of people swear by it.
Hope this helps