I started to read "Types and Programming Languages" by Benjamin Pierce, and was immediately struck by the exceptional clarity of this author. I can almost recommend anything by him sight unseen, especially after I picked this concise paper on the lambda and the pi calculus off his website. If you want to firm up your grasp on foundations of programming, go, get, read; do not delay, do not let the book sit around on your shelf for months the way I did :)