Thanks to Brad Snyder for this one:
Nick Potter has created a set of free Keyword lists for Lightroom. The lists cover Geography, Animals, Colours, Natural Landforms and Bodies of Water. While not proclaimed as a comprehensive list, it’s certainly cheaper than the Controlled Vocabulary list created by David Riecks. That said, David’s list is far more comprehensive. Even more comprehensive is Shangara Singh’s Keyword Catalog.
Why Lists in the first place? Well, auto completion is a good reason, as it saves typing. Also when you run through a specific list, it helps keep your keywords tidy.