PWM wouldn't be my first choice for controlling a fan, because the fan may start behaving erratically due to the frequency. I'm going to assume that the products to which you've provided a link have addressed this issue, which is really a minor one.
A rheobus is far simpler and cheaper. It's a nice medium between the rheostat and the PWM controller. The rheostat is not energy efficient.
As for fans, I have yet to pick it up, but I am going with an automotive "squirrel-cage" type blower. The advantages include lower noise per cfm, and more importantly, they are able to create good flow with much more pressure than what an axial fan can do.
Check out Delta's lineup, at
www.deltaww.com .