Junior to mid-level developers - GO READ "CAREER CALCULUS" NOW!
I usually try not to be the 88th person to link to the same article, but this one is definitely worth it. A real gem. Every single word. And despite the fact that most of you don't know who the hell I am or what I do, just let me tell you that I got where I am today (which is exactly where I want to be!) by being faithful to the principles described by Eric in Career Calculus.
If you are still early in your career, this is a MUST read!