- Anything from Ryan Singer of Basecamp I would highly recommend. He talks about understanding an interface as a "job to be done", a paradigm I've found most helpful. He also has an excellent talk on designing with forces, a way of thinking about a solution as the result of all the forces in play in a problem scope.
- Whitney Hess, a UI/UX consultant has some GREAT material on understanding the necessity of empathy in design and design as problem solving.
- There's a great little book to spark your thinking on problem solving in design called "Are your lights on" - Pretty entertaining too :)
- Tools to discover more about your users and help guide design process:
- empathy map
- user personas
- https://twitter.com/KentBeck - pioneer of extreme programming (i.e. agile), now works for facebook
- https://twitter.com/martinfowler - wrote Patterns of Enterprise Application Architecture & worked with Beck on XP