Each show i listen to generally will have a primary sponser, who writes the show "headline song" and generally that sponsor will write lyrics to make that a jingle that has to do with their product.

Then you get the intro to the show, and sometimes a product spot. Then the show starts, and depending on the format (half hour, multi-part 12 minute, etc) you may get a mid-roll and finally at the end a final sponsor message, plus the studio (like CBS) would pitch other shows on their network, and the star of the show would also have their current movies and other productions pitched at the end, as well.

Check out Richard Rogue on OTRR or archive.org for both styles, the mid-roll and the post-intro roll with jingle, it varies depending on year of production. Their main sponsor was Fitch, as far as i can tell.