Steven Pinker's "The Language Instinct: How the Mind Creates Language" is a thought-provoking look at the psychology of language learning. Drawing on Chomsky's work, Pinker's hypothesis is that we as humans have a universal 'instinct' for language interpretation - in the same way that spiders have the instinct to spin webs.
In this work, Pinker argues that rather than being influenced by external factors, we are actually all born with a predisposition towards language as a method of communication. This book touches on some of the most controversial issues in modern linguistic theory - Chomsky and Pinker have both strong supporters and opponents in the field, and in light of this, neither should be taken as a definitive authority.
However, this is one of the best introductions to the psychology of linguistics currently available, and along with Chomsky is often set as recommended reading for both psychology and linguistics students alike. Highly recommended for anyone who would like to dig a little deeper into the most controversial issues currently being debated in the field of linguistics.