I recommend Bill Buxton's Sketching User Experiences as a important book to read.

It very much pushes on the way both the imagined end result and the tools at hand play a huge part in the success or failure of a design. It has totally changed my mindset.

Tufte has become an icon for me in the space that often gets reduced to infographics, but really has to do with the meaning available through comparisons.

One of the concepts that came to me from him is roughly "information is all the differences that make a difference." And this title of his, Envisioning Information, explores the way changes and similarities, represented visually makes information accessible in ways numerical abstractions sometimes hide.

A further extension on this thought, is the way images and the information contained in them can be the heartbeat of a power, convincing and compelling narrative. His Visual Explanations challenges a lot of the notions I had about important and help me refine a key idea for all of my interaction and information designs: salience.

For the actual work of designing interfaces, Kim Goodwin's Designing for the Digital Age and Robert Hoekman, Jr.'s Designing the Moment have formed the basis for my process, moving from strategies and concepts through user insights to frameworks structures and finally interfaces.