At work, we have what we call our module library, which is an interface with which to browse (and edit) the snippets of code and style (we call them modules) that we use to make up our site. They’re not templates, as such, but rather starting points for the blocks with which we build our pages.
Dan Cederhom of Simplebits has just announced his release of a WordPress theme that you can use to create your own pattern library.
It’s called Pears.
He’s hosting it on github, so you can tweak/improve it as you will.