I've had a chance to look over The Ultimate Martial Arts Encyclopedia, and its not all that I'd hoped and dreamed. Its not an encyclopedia per se but rather a collection of reprints from Inside Kung-Fu and Inside Karate. There are a few articles on combat systems originating outside of Asia, but the book is still heavily focused on the arts of East Asia. Disappointed, but undaunted, I looked in a couple of book stores, new and used, to see if there is anything to be found that deals with non-Asian martial arts in a substantive fashion. Barring books on capoeira and jiu jitsu, of which there are plenty, there seems to be a dearth of material on non-Asian practices. This gives me hope that I'm engaging in a worthwhile endeavor and not just re-inventing the wheel.
At the same time, while perusing the UMAE, I've come to the realization that its not going to be sufficient to try to identify representative arts from different regions. For one thing there's the ever-present difficulty of tryingto determine what qualifies as "representative". Even if you managed to do so you'd end up with a (rather large, I imagine) list practices without any overriding sense of order.
It seems to me at this point that, if we're going to talk about comparative martial arts, the best way to start out will be to assemble a fairly exhaustive list of current practices and trace their lineages back into the past. I expect that this process will be analagous, in many respects, to tracing the development of languages, since up until fairly recently both have followed similar patterns of geographic diffusion and mutation over time. Like languages, I expect that martial arts will naturally fall in to families that share certain characteristics, and that performing inter- and intra-family comparisons will go a long way towards helping us suss out the water and flour of the martial arts.
The next task, then, will be to assemble our list of current practices. In this endeavor the UMAE will undoubtfully be helpful, as will the various resources scattered willy-nilly over the vastness of the Internet.