Sacha Greif
A Few Psychology and Behavioral Economics Resources
Instead of reading about design, these days I'd rather read about psychology. I find understanding the underlying mechanisms of the brain fascinating, especially when it comes to biases and fallacies. 
And actually, the more I read, the more I see how psychology shapes design. In fact, one of my projects would be to compile as many psychological studies and examples as I can, and then map each one of them to a practical design or marketing example. This would make for a great book/blog/online course, if only I had the time…
Anyway in the meantime, I wanted to share a few books and resources with you (and hopefully receive a few suggestions in return, too!) 
Influence: The Psychology of Persuasion
Robert Cialdini's book is probably one of the best-known, most approachable, and most practical psychology books you'll find. 
The reason it's so famous is that being all about persuasion, it applies directly to sales and marketing. Or alternatively, to manipulating your friends and family into doing your bidding.
Just kidding, reading psychology books won't turn you into a sociopath (although it might very well turn a sociopath into a more effective sociopath).
So I definitely recommend reading this book, and seeing if you can use its teachings to improve the effectiveness of your designs.
Dan Ariely's Online Video Class
Dan Ariely is a one-man-army of behavioral economics: he has a blog, a weekly column a couple books, and an awesome free video class
I suggest reading his blog and books, but I strongly recommend you join the class: you'll get a crash course in behavioral economics with tons of practical advice, especially regarding the psychology of money.
And did I mention it's free?
Camels and Rubber Duckies
Thanks to this post by Joel Spolsky, I finally understood what market segmentation is, a.k.a. the reason why supermarkets stock 15 different brands of potato chips (or in my case, 15 different kinds of tofu). 
I don't know if you'd classify it as marketing, economics, or psychology, but understanding market segmentation is a powerful thing, and one that directly translates into the amount of cash in your wallet. 
Thinking, Fast and Slow
Daniel Kahneman is a Nobel-prize winning psychologist, and his book provides a framework for understanding all of our biases and fallacies, based around the idea of our brain being regulated by a fast-acting yet dumb "System 1", and a more methodical (but slower) "System 2".
The book is not that easy to digest, so I would not suggest it as your first psychology book. Still, once you feel you're ready for it, this book will make you realize your own stupidity like no other. 

Drive Animation

This nifty animation exposes the central themes of Drive, Daniel Pink's book about motivation.

No need to read the book, just take 10 minutes to watch the video and save yourself some time! (although maybe the book is great, I wouldn't know since I watched the video instead…).
Malcolm Gladwell-style Books
These books take one central idea ("we make snap judgments", "influencers are important", "aliens built the pyramids") and then drown you in an avalanche of studies and anecdotes to support that theory. In my opinion, they're mostly bullshit. 
As Daniel Kahneman point out in his book, the brain suffers from the "what you see is all there is" (WYSIATI) illusion. Meaning that if all I do for a whole book is only provide you with evidence supporting a theory, you'll generally accept it as true and never question the fact that I conveniently forgot to address any contradicting evidence. 
There's a fine line between discussing a topic ("how does influence work?") and promoting a pre-established theory ("influence works like this, and here's some proof"). I try to avoid books that take the second approach, unless they're written by Nobel prize winners. 
More Books
If you want more, GoodReads has a list of popular psychology books. And to my surprise, so does Google!

What about you, do you have any good psychology resources to suggest? And has knowing about psychology helped you with design, sales, or marketing?