mullr

The Pragmatic Programmer (Read this once every 6 months until it's obvious)

Head first design patterns

The Non-Designer's design book has helped me 1 of every 5 days in the past month. I also recommend it.

Agile Web Development with Rails It's not obvious, but the rails book is a great introduction to test-driven development in general.

"The Lightning Tamers", by Kathy Joseph, is a wonderful and accessible book about the history of electricity.