Although New York-based designer and educator Allan Chochinov claims to dislike the word 'manifesto', this hasn't stopped him from writing one.
1000 Words: A Manifesto for Sustainability in Design includes such points as being Hippocratic before Socratic ("First, do no harm"), thinking about systems before artifacts and designing for impermanence.
"The power of design is an amazing thing. Let's wield it wisely."