[nana_gb]

Influence: The Psychology of Persuasion by Cialdini is one of my favorites

Also Predictably Irrational by Dan Ariely he's got a great blog too http://danariely.com/ make sure to check out the videos section

[MaysonL]

Ditto to both of those.

Also: The User Illusion: Cutting Consciousness Down to Size, by Tor Nørretranders.