If there is a Radio Shack near you pick up a copy of their "Police Call" directory. The new 2005 book probably isn't out out yet, but they may have some 2004s left.
The first part of it explains pretty much all aspects of scanning and how radio systems and radio waves and all of that good stuff works. It also contains frequency information obtained from the FCC Database, all licensed frequencies for municipalities, plus a section that contains frequencies for commercial businesses like bus, taxi and limousine companies, malls, newspapers, and a bunch of other stuff. Give it a shot.