'Team Geek' is a great primer on technical leadership: http://shop.oreilly.com/product/0636920018025.do
Another recommended book is 'Shipping Greatness': http://shippinggreatness.com
Assuming you're already familiar with 'The Lean Startup', there has been a series of excellent 'sequels' on many more specific disciplines that you will likely find useful: http://theleanstartup.com/the-lean-series
A recent addition (that I am still digesting) on Agile processes beyond Scrum is 'Unblock!': http://www.continuousagile.com/unblock/ (Posted to HN a few days ago: https://news.ycombinator.com/item?id=7921200)