I agree with many of the mentions (Little Schemer is almost omnipresent), but would like to add a newer book: Growing Object Oriented Software Guided by Tests. The title may mislead one to think the book is a dry repetition of the same-old "OO principles", but it isn' so. The meat of the book is a step-by-step description of the development (through TDD) of a largish application; and somehow they managed to make the whole thing interesting. I wish more books would take on a large development endeavor in a narrative way.

edit: grammar