A few links for the linguistically inclined, from "The Exvulsion of the Blatant Beast". First, a couple of fascinating posts from a while back on the evolution of the Celtic languages: here and here (I would have linked to these sooner, but the background color on the site has been ... strange ... lately, and I couldn't stand to look at it long enough to find the links again).
Then, for the really ambitious (also courtesy of "Beast"): Early Indo-European Online. No Old Welsh, unfortunately... but then modern Welsh is keeping me busy enough at the moment.
More on that later, though.