I'm sure guys like Freud, Jung, Weber, Marx, and Durkheim had some interesting ideas. I'd like to know what those ideas were, and why people at the time took them so seriously.

So... my opinion here is generally, if someone is worth reading the originals, you'd know already. It is worth reading The Wealth Of Nations, because Adam Smith was that clever and that comprehensive. Is it worth reading Marx? Well... not really. His method of explanation is pretty poor, actually.

With Freud, you have one core insight that is truly revolutionary (the primary human drive is libido) and then a bunch of mind projection fallacy. Humans actually have an anti-incest impulse such that they don't find people they grew up around attractive. Freud's mother was totally hot, though (or something), and so Freud projected his Oedipus complex onto everyone else. The rest of what he posited is generally totally wrong. (Not as familiar with Jung / Weber / Durkheim.)

And so if someone asks me whether they should read Smith xor Hayek, I have a hard time answering. If someone asks me whether they should read Darwin xor Dawkins, I favor Dawkins (but haven't read much of Darwin). When someone asks me whether they should read modern psychology xor Freud, there's no contest. You could read something like The Red Queen by Ridley and get a much fuller expansion of Freud's insight than you could by reading Freud.

(xor = exclusive or; if it's regular or, the answer for the first one, at least, is "both!")