The producers of 'Mad Men' paid a fortune for just a snatch of "Tomorrow Never Knows" by The Beatles for use near the end of the episode. Any piece of psychedlia music might have worked in showing how disconnected Don Draper has become with the times (which are a-changin'), but it was important and integral to the plot that it should be the Beatles. In the advertising game, they would want nothing but the best to promote their clients.
Here's the song in full:
Don couldn't make it past one minute of the song....