jerf

I've often recommend SICP to self-taught programmers; it is not a complete substitute for a computer science education, but it is a concentrated dose of the stuff you're probably missing out on.

If you actually finish that book you'll be ahead of the vast bulk of programmers

Personally, I don't recommend the SICP unless you're actually working through the exercises to some extent

Godel, Escher, Bach (mentioned by caffeine) is a love it or hate it book; check out a couple of summaries and see what you think.

and The Pragmatic Programmer

Already mentioned is Code Complete

I'd add The Mythical Man Month, still a classic, but note that's a relatively short book and may not last long enough.