SICP has already been mentioned a couple of times and I agree with that 100%. What I find helps me more than anything to be a better programmer is to find those gems that take you out of your day-to-day routine and help you see programming in a different way. So a couple of other books I’d throw in with SICP are “The art of Prolog” and “The Little Schemer.” I still today admire Prolog’s declarative style so much today. Even though I haven’t had the opportunity to use it professionally, I still come back to it now and then to refresh on it.