The wonderful Little House in the Suburbs blog has shared three posts on companion planting:

• Part 1 – covers the rule “Too many members of the same family shouldn’t be seated together.”
• Part 2 – covers the rule “Hatfields and McCoys must be kept across the room from each other.”
• Part 3 – covers the rule “Sometimes somebody dated someone else’s sister and it ended badly, so those individuals need to be kept apart.”

Part 3 contains a tremdendous chart that gives an at-a-glance summary of the rules, invaluable for any home gardener.