High level overview of user research, lays out several dimensions: attitudinal/behavioral, qualitative/quantitative, context of product use, as well as how research approaches vary based on your stage in the product cycle.

Another favorite blog post on product design focused on how you define the problem you are solving to begin with and how to develop a product concept.

Really great piece, although a bit academic, laying out a framework for thinking about different kinds of prototypes and how you can use them to communicate and answer questions.

Basic introduction to usability concepts.

Tips on designing a usability test.

Explanation of the “think aloud protocol” which is an extremely simple and effective technique for conducting moderated research.

Simple techniques for interrupting or asking users questions during a session.

Bunch of solid recruiting tips.

Handy roundup of remote research tools.