Citation graph, a graph of academic papers and their citations to each other.
Double Bubble conjecture (now a theorem), the fact that the minimum-surface-area enclosure for any two volumes takes the form of three spherical patches meeting in a circle.
They're all a bit short, in need of more detail and better illustrations, but still I think more useful than not having an article at all.
The double bubble article perhaps needs a little hint as to how a double bubble can consist of three spherical surfaces. (I worked it out in the end: the flat disk separating the two bubbles in the equal volumes case is part of a sphere with infinite radius.)
Thanks for the suggestion; I've rewritten that part in an attempt to clarify it.