I found a gold mine of articles by Eric Boehlert for Salon about Clear Channel's Radio Monopoly:
Radio's big bully.

Highlights include: background on how Clear Channel and how it managed to quietly take over radio (the company owns nearly 1,200 radio stations and effectively controls the rock radio market and also owns SFX Entertainment, the nation's dominant concert-venue owner and touring promoter), the corporation's evolution under the aegis of Randy Michaels, the "new payola" (the complex arrangements under which the world's major record companies pay for virtually every rock song broadcast on commercial radio) and links to the Clear Channel Web site so you can locate the affiliates nearest you (there are probably a ton of them right in your town!).