I just received in the mail an unsolicited examination copy of The Quantum Challenge: Modern Research on the Foundations of Quantum Mechanics (2nd ed.), by George Greenstein and Arthur Zajonc (Jones and Bartlett, 2006 ). I haven't had a chance to do more than skim through it yet, but already I'm very impressed. I think this book would be very appropriate for anyone interested in topics like Bell's Theorem, evidence for existence of photons, Schrödinger's cat and the "measurement problem." Despite the forbidding title, it's actually written at an advanced-undergraduate level, as an introduction to these issues. It's not very heavy on equations, and the text is well-written and easy to read, although understanding this stuff takes some work and mind-stretching if you're a newcomer to this area, of course! [added] If you search for this on amazon.com, beware that the main listing is for the first edition from 1997. I eventually found that they do have the new edition, by following a link in the "other editions" section.