I recommend Barry Boehm's book on the subject: Balancing Agility and Discipline: A Guide for the Perplexed, ISBN: 0321186125 . I've used Barry's advise for discussing the right level of agility and discipline whit stakeholders. Espacially in projects with special quality assurance requirements. See also CombiningXpWithQualityAssurance.
Incidently, here's my comment on Barry's analogy with the elephant and the monkey:
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