From the venerable Dieter Rams:

• Good design should be innovative
• Good design should make a product useful
• Good design is aesthetic design
• Good design will make a product understandable
• Good design is honest
• Good design is unobtrusive
• Good design is long lived
• Good design is consistent in every details
• Good design should be environmentally friendly
• Good design is as little design as possible

[Via GigaOM]