Here are a few web sites that may be of interest to you...
The Pipe Organ Education Projectís goal is to kindle interest in the pipe organ. The site explains how an organ works and provides other interesting information on pipe organs
This was designed to teach children about pipe organs but it can also be quite informative to adults who would like to know more about pipe organs.
The Encyclopedia of Organs stops has a lot of detailed information on various of organ stops. All are listed alphabetically so you can look up the name and read the details of a particular stop http://www.organstops.org/