The AIM, or Aeronautical Information Manual is a regularly updated textbook on US flight procedures. It covers everything from airmanship to zulu time, and has been available for free, online, for years. After years of killing many trees, Transport Canada has released our equivalent, the Aeronautical Information Publication on the net too, but only in PDF form. This link takes you to an HTML-converted version of the 2004-4 edition, as generated by pdftohtml, a nifty little tool.