For example: I've heard vague rumors that GWF Hegel concludes that the Prussian State (under which, coincidentally, he lived) was the best form of human existence. I've also heard that Descartes "proves" that God exists. Now, whether or not Hegel or Descartes may have had any valid insights, this is enough to tell me that it's not worth my time to go looking for them.

This is an understandable sentiment, but it's pretty harsh. Everybody makes mistakes -- there is no such thing as a perfect scholar, or perfect author. And I think that when Descartes is studied, there is usually a good deal of critique and rejection of his ideas. But there's still a lot of good stuff there, in the end.

What philosophical works and authors have you found especially valuable, for whatever reason?

I have found Foucault to be a very interesting modern philosopher/historian. His book, I believe entitled "Madness and civilization", (translated from French), strikes me as a highly impressive analysis on many different levels. His writing style is striking, and his concentration on motivation and purpose goes very, very deep.