We have an emotional and a rational side (they are not left-right) and this has been understood and written about for centuries. But now we have neuroscience and many clever people who dream up and conduct very clever experiments. And we have writers like Jonah Lehrer who put it all together in readable prose. His How We Decide is light reading for smart people. That is very high praise.
There are now many books that cover similar territory, but this one is (in my view) the best. The author covers decision making by airline pilots, athletes, singers, voters, shoppers, investors, generals, gamblers and others. He knows enough about the current science to clearly explain the successes and the failures in each field.
The emotions and the intellect can work wonders if they interact properly. And that's a big "if". Read the book (Spock!) to get the full story.
I am also reminded of Vernon Smith's criticism (this econtalk interview) of the many experiments that find us so irrational. The experiements have us make decisions and choices solo that we actually always make after some deliberation and consultation with friends and family. That part never gets into the laboratory and it undermines some of the findings.