SICP is a classic I can highly recommend. It made me aware of just how much the "new, smart" approaches to organizing code that people like to attribute to their favourite programming model (like "OOP is best because classes and inheritance means modularity") are actually rehashing of obvious and general ideas known very well in the past.

I generally like reading on anything Lisp-related, as this family of languages is still pretty much direct heritage of the golden ages.

The stuff done by Alan Kay, et al. over at PARC is also quite insightful.