Just had an idea...why not just use a regular adjustable power supply? Cut off the connector, attach a fan plug, feed it through a hole in the case, and you have an externally controlled fan, and you also lower the power consumption on your PSU.
http://www.radioshack.com/product.asp?c ... 273%2D1662
Easy Fan Control
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How about an old "Power Pack" from some HO model trains (N scale may not have enough output). These things plug into the 120v line and put out a fixed AC which you don't need and a variable DC (0 to 12-14v) to the tracks. Why it even has a "reversing" switch in case you need to change the inlet fans to exhaust and exhaust to inlet. Check out the garage/lawn sales this spring.
Why you can set two different voltages with this one and probably one amp output on each. And then there is 5v fixed from the ATX PSU. Maybe I'll pass on the Sonata with the "fan only" leads from it's PSU and get a big tower with a lot of 80mm fans 