Ethnographers tend to be rather hands off (/against) directly changing who they're observing. Contextual Inquiry (http://www.usabilitynet.org/tools/contextualinquiry.htm, http://www.amazon.com/Contextual-Design-Customer-Centered-In...) is a fairly light weight method and I think would benefit a lot of startups.

1. [Visual Grammar](http://books.google.com/books/about/VISUAL_GRAMMAR.html?id=w...) by Christian Leborg

2. [Emotional Design: Why We Love (or Hate) Everyday Things](http://www.amazon.com/exec/obidos/tg/detail/-/0465051359/) by Don Norman

3. [The Elements of Typographic Style](http://www.amazon.com/Elements-Typographic-Style-Robert-Brin...) by Robert Bringhurst

4. [Grid Systems](http://www.amazon.com/Systems-Graphic-Systeme-Visuele-Gestal...) by Josef Muller-Brockmann

5. [Ordering Disorder: Grid Principles for Web Design](http://www.amazon.com/Ordering-Disorder-Principles-Design-Vo...) by Khoi Vinh

6. [Why Customers Really Buy: Uncovering the Emotional Triggers That Drive Sales](http://www.amazon.com/Why-Customers-Really-Buy-Uncovering/dp...) by Linda Goodman (I've had the pleasure of meeting her and overhearing her office conversation during my daily tasks at the office in Houston, where she worked for a spell. Incredibly sharp, and it is clear that her principles exposed in this book are thorough-going in her interactions with people. I think it would be important to apply her research to Lean methodologies, building Features only around Emotional Triggers. This is what we are aiming at, but I am making this connection right now, I believe, in saying this.)

7. [Contextual Design: Defining Customer-Centered Systems](http://www.amazon.com/Contextual-Design-Customer-Centered-In...) by Hugh Beyer, Karen Holtzblatt

My favorite UX books:

The Design of Everyday Things (http://www.amazon.com/Design-Everyday-Things-Donald-Norman/d...)

The Humane Interface (http://www.amazon.com/Humane-Interface-Directions-Designing-...)

Contextual Design (http://www.amazon.com/Contextual-Design-Customer-Centered-In...)