Code: The Hidden Language of Computer Hardware and Software was one of the most formative books for my programming self education. I've tried to loan it to several of my friends more than once, and it was a gift to me. Also had a strange case of loaning out C# 4.0 in a Nutshell and never getting it back, but I would do it again (with an updated version). Albahari is good at writing a reference without being too boring, and C# has some legitimately interesting sides in how it does some things, like it's dynamically compiled regexen.
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