Generating new business ideas
The Innovator's DNA - A classic on the 5 "discovery skills" of innovators
HBR article by Daniel Gulati on five sources of startup ideas
The different steps of design thinking, interview with David Kelley, founder of the Stanford d.school
Evaluating new business ideas
Excellent advice on How to Get Startup Ideas and Evaluate them (including 4 most common mistakes) by Jared Friedman, Partner at Y Combinator: article & video
More on evaluating startup ideas including five potential sources of "unfair advantage", talk by Kevin Hale (YCombinator)
The qualities of a clear business opportunities, simple but valid insights from a consultantÂ