If you're interested in media history at all, you should already have a copy of On The Air by John Dunning. One of the most comprehensive reference works on the type of radio program the broadcast networks presented in pre-TV days, I can't recommend it highly enough, but if you had to have it on the day it came out, you bought it through Amazon with the exact same $13 discount they're still offering off of list price eight years later. This is why I'm jealous as hell that the book is now being offered directly from the publisher for under $20 for what I assume will be a limited time.
Totally serial, folks, if you've ever been interested in the Depression-through-postwar era, broadcasting, or just want some evidence for your tedious "it's been done before" rants (and I'll be getting to those again before too long), you should make room on your bookshelf for On The Air. Not only is it full of useful information about famous and obscure radio shows, but it's written in a style which makes it great pleasure reading, too.
And of course, the standard disclaimer: I am not affiliated with Oxford University Press in any way and I don't get any money for this plug. So there.