FoamTree: Visualize hierarchical data with a lot of groups
It's a Voronoi Treemap, which sure, looks kind of neat, but the nice part is how well it handles large amounts of groups. It's puts off computation and rendering until it's needed, so it cuts down on load and run times. Just check out the Tree of Life demo and select "Homo sapiens" in the ride sidebar to see how it works.
The library is free to download, but you have to pay a license fee to get rid of the branding.