James prepared a popular abridged version of Principles which may be just as useful. (Disclaimer: I've only read the abridged version, so I don't know what's missing from the full two-volume version.) It's a very practical and introspective approach to psychology, somewhere between pop science and intellectual self-help. I think HNers would enjoy it.

Here it is on Amazon for $0.99: http://www.amazon.com/William-James-Psychology/dp/B000W2GH4E

Here's an online version: http://archive.org/details/psychologybriefe00willuoft