It's much easier to create a calm, elegant interface when your content is simple and static, but in some web applications, the content and interactions are inherently more complicated and dynamic.
What are some examples of web applications that manage to make complex content and interactions feel calm and orderly without sacrificing functionality?
For instance, I remain impressed with Gmail, which may not be beautiful, but densely packs functionality into a calm interface (whereas even the latest beta of Yahoo! mail continues to feel loud and obnoxious).