My two examples are interesting as they sort of present contrasting attributes of desirability: exclusivity vs. familiarity.
Harvard is a very desirable brand when it comes to education. It has a very prestigious reputation when it comes to the quality of education, the intellectual environment offered by the students, the rigor and stimulation provided by the professors, and the opportunities that are opened after getting that diploma. And this creates a cycle of maintaining this position in higher education, keeping the desirability of the “brand name”, not just with its students, faculty, staff, and affiliates, but also with the wider audience (applicants, parents, media, other members of the academe, etc.) Its greatest appeal is this perception of exclusivity, it’s status of being excellent or elite.
Sesame Street is another thing that I think is designed pretty well. Quality programming is their major strong point, as they are really proud of their rigorous model of developing and creating educational yet engaging television shows for children. The use of the furry and funny muppets is what appeals to the young audiences, which sticks when they grow up, creating this loyalty towards the show. Adults who grew up watching Sesame Street would always feel this nostalgia whenever they see an image of Big Bird, or maybe Oscar the grouch. It has a certain emotional familiarity that makes it very popular to both parents and children.