Learn to program. Seriously. I know this isn't the answer you're expecting, but there is nothing you can do that will better prepare you to manage developers.<p>I managed one very technically complex product (VPS service like Slicehost/Rackspace, where the customers were also developers) and one consumer based product (micropayment provider for social games before I finally bit the bullet and learned to program (I'm now the hustler and one of the hackers at a startup I founded)<p>I would have been far far more effective at those previous two positions if I knew then what I know today.<p>My recommendation, especially if you work with any product where the interface and user experience matters, is to learn Javascript. Specifically, I would suggest Eloquent Javascript by M. Haverbeke.
Some of the best:<p>- The Pragmatic Programmer: From Journeyman to Master
- Code Complete: A Practical Handbook of Software Construction
- Joel on Software: And on Diverse and Occasionally Related Matters That Will Prove of Interest to Software Developers, Designers, and Managers, and to Those Who, Whether by Good Fortune or Ill Luck, Work with Them in Some Capacity