19. There's Multiple Underdog Productions Logos
If you're the sort of person who doesn't immediately change the channel the moment the credits roll, then you'll be very familiar with the Underdog Productions card. A subgroup of Fuzzy Door Productions made specifically to produce American Dad, their post-credits title card features a security guard (named Peña, who used to work at the studio), saying goodbye to the audience. It's so fleeting a moment that it's easy to miss that it's not the same farewell each time.
There's in fact four different versions, all variations of the one that immediately pops into your head when you see him ("Bye, have a great time!", with either "wonderful" or "beautiful" replacing "great", or the more simplistic "Have a great night!"). It's not quite Chuck Lorre's vanity cards, but it's still pretty cool.