20 of 20 Corrected image description

Eldarerathis summarized it very well. To add some things: The 1.1 version was internally called Petit Four by Google, and that's how it all began. Google is installing a giant pastry on their lawn at Mountain View each time a new version is about to be launched.

You can see pictures of that display at different stages here:

Overall display (Cupcake to Eclair, with Nexus One) Donut, Android logo, Nexus one, Cupcake, Eclair

HoneycombFroyo

Eclair, Froyo, Gingerbread, Honeycomb and Ice Cream Sandwich Gingerbread, Icecream Sandwich, Honeycomb

Kit-Kat KitKat, Jellybean

Lollipop Lollipop

Marshmallow Marshmallow

Nougat Nougat

Oreo Oreo