Here's an introduction to a special kind of exhaust fan -- an "In-Line" fan. This means that rather than having the motor right at the ceiling, they can be placed anywhere along the line of the ductwork. This makes their installation much more flexible, and quieter. Equipment details can be found at Continental Fan.
Clothes dryers require special in-line fans to avoid lint build-up on the fan blades and handle the temperatures of the clothes dryer itself -- follow this link for details.