The key to the TARDIS has regenerated nearly as much as the Doctor has.
Close your eyes. Now imagine you are standing in front of the TARDIS. You've got something in your pocket -- it's the key to your own Type 40. Reach into your pocket, take it out, and look at it.
What does it look like? Well, that probably depends on when you first saw an episode of Doctor Who. There have been all kinds of versions of the TARDIS key, some normal, some ... peculiar. And now here they are, all in one place, along with who was the owner of each.
I grew up with (and even owned my own version of) the Fourth Doctor's TARDIS key. How about you?