1. The World and the West- Arnold Toynbee
Toynbee's become one of my favorite historians, and takes a sober but unsentimental view of the effects wrought throughout the world arrising from its encounter with Western Europe. Tastefully restrained, avoids forays into propagandistic revisionism of either the Right or the Left.
Read this when I was a junior in high school, but enjoyed it more the second time. The German philosopher Hegel made a great point about this play- that it is the supreme classical tragedy because the opposed forces in it are both striving for two forms of Good, and so Good must necessarily be a victim in the dramatic contest.
3. Essays of Robert Louis Stevenson
The problem that comes from being known as an author of boys' adventure novels is that no matter how masterful a prose stylist you are, critics will always give you the short shrift. Stevenson is one of the victims of the fact. The man was a dauphin of non-fiction as well as a rousing storyteller, and if you haven't read any of his essays, "Aes Triplex" ("Triple-brass") is a good place to start.
4. The Ordeal of Richard Feverell- George Meredith
Meredith is an odd duck of a novelist; he's a Victorian, but not much for moralizing, which puts him at odds with most of his contemporaries. This story is a mock-melodrama about a boy whose father's brutally individualistic system of private education makes him into an antisocial arrogant jackass. Not a great novel, but it has some entertaining comic episodes and dialogue. A better starting place for Meredith, if you are thus inclined, would be "The Egoist." Also a fine poet.