One of the greatest success stories on the Web must be Jim Romenesko's daily roundup of media industry news, under the aegis of the Poynter Institute. Crisply written and totally in touch, it's indispensible.
For news about radio I check the home page of the industry publication "Radio and Records."
The weekly NPR show "On the Media" takes a consistently fresh look at the media, and the Website makes it easy to listen to segments of the show if you don't find it on your local public radio station.
Among the best media critics around is the Los Angeles Times' Tim Rutten, who writes its "Regarding Media" column twice a week.
And some of the most entertaining and penetrating coverage of the media comes from satirist Harry Shearer on his weekly radio program "Le Show," originating from the fertile ground of KCRW Radio in Santa Monica, California and broadcast nationally. Current and past shows can be heard online through the Website.
To keep up on current books, performers, and issues in the arts, I listen when I can to Leonard Lopate from New York's WNYC. The media are not the main focus, but the show is brilliant, always timely and well-researched, and with terrific guests. As an interviewer, Lopate is in a class by himself: curious, witty, articulate, extraordinarly well-informed, a superb listener. It's one of life's great mysteries that his show is not broadcast nationally, but at least it's streamed on the Web.