The Lean Startup By Eric Ries
The Lean Startup is the current hot book on the topic. It is a good strategic overview of the conversation and it puts a lot of the pieces in perspective.
The 4 steps to the Epiphany by Stephen Blank
The 4 steps is the seminal book for this area. This is Lean Startup Before it was Lean startup and it covers some very important tactical issues around how to approach the market place directly.It is a bit of work to go thru, but it is worth the effort.
The Entrepreneurs Guide to Customer Development by Patrick Vlaskovits
This is the Cliff-notes version of the 4 Steps. It helps simplify and focus some of the conversation.
Business Model Generation by Alexander Osterwalder
The Business Model Generation is a fun crowdsourced book aiming at focusing on the process of getting the right questions answered for your business and getting clarity on your business model.
Running Lean by Ash Maurya
Running Lean is a story of the journey for a startup software company using the 4 steps and the Business model generation to get to the end. Ash tells an interesting pattern and it leads to the Lean Canvas. I have used http://www.leancanvas.com often to help focus the conversation about a startup.
Personal Kanban by Jim Benson
One of the hardest things for entrepreneurs is to focus on the right thing. Personal Kanban presents an interesting method of keeping focus and getting teams to play together and to as a group focus on what they need in order to make rapid progress.