I've been working on a page including information on some formal troubleshooting methods. En route, I have been looking at Cause-and-Effect (Ishikawa fishbone) diagrams and Interrelationship Diagrams.
Here are some of the noteworthy web pages I've been looking at:
Concordia: Cause and Effect Diagram and
Concordia Interrelationship Diagram provide a nice introduction to the two types of diagrams.
HCI Cause and Effect Diagram provides a slightly longer article, including some historical informaton about Ishikawa diagrams.
balancedscorecard.org Cause and Effect Diagram provides a much more in-depth view of Ishikawa diagrams.
questlearningskills.org Interrelationship Diagrams provides a howto level article about Interrelationship diagrams.
ASQ Interrelationship Diagrams provides a slightly longer article about Interrelationship Diagrams.
Root Cause Analysis: A Framework for Tool Selection provides a nice comparison of Ishikawa and Interrelationship diagrams, as well as Current Reality diagrams.