[henrik_w]

"Explore It" by Elisabeth Hendrickson [1] is a short, easy-to-read introduction to exploratory testing ("manual testing") that has many concrete ideas for what and how to test SW.

[1] http://www.amazon.com/Explore-Increase-Confidence-Explorator...

[jacques_chester]

Related is the "Test Heuristics Cheat Sheet" [1] that she and others put together.

[1] http://testobsessed.com/wp-content/uploads/2011/04/testheuri...