This might be old hat for the crowd here, but I've just discovered Karl Popper and I'm working through his collection of talks and essays, "Conjectures and Refutations." It contains a lot of very clear insights about the philosophy of science and its application to political and historical questions; the two most interesting pieces to me so far were one on Hume's problem of induction, discussing the difference between acceptance and logical certainty, and one on the development of the scientific mindset in Greek-era philosophers. I strongly recommend it if you're interested in such topics.

I also recently read Marvin Minsky's "Society of Mind", which is just a fantastic book. It's a very fleshed out introduction to some of Minsky's ideas about how surface-level phenomena of the mind like memory, learning, and volition can be explained through a model of the mind as a hierarchy of tiny agents with very specific goals that communicate among themselves. It's amazingly written; completely accessible, written in simple language, but every paragraph has a thought-provoking concept about something or other. (The single flaw is that it doesn't really reference a lot of actual research or data; it's more or less just laying out some food for thought based on our intuitive understanding of our mind.) I would pretty much recommend it to anyone at all.

Finally, I read Hermann Hesse's "The Glass Bead Game" -- although Hesse has been a favorite of mine for a long time, I never got around to that one -- and I found it to be the best fiction I've read in a year or two. You can head to wherever for a summary, but I highly recommend it to anyone. I suspect the premise will especially appeal to the sort of systematizing, truth-seeking folks around here.