The BBC's Fifteen Web Principles. The others are good suggestions too, but these resonate with what a good web site should be/do.
1. Build web products that meet audience needs: anticipate needs not yet fully articulated by audiences, then meet them with products that set new standards. (nicked from Google)
2. The very best websites do one thing really, really well: do less, but execute perfectly. (again, nicked from Google, with a tip of the hat to Jason Fried)
3. Do not attempt to do everything yourselves: link to other high-quality sites instead. Your users will thank you. Use other people's content and tools to enhance your site, and vice versa.
6. The web is a conversation. Join in: Adopt a relaxed, conversational tone. Admit your mistakes.
8. Make sure all your content can be linked to, forever.
11. Consistent design and navigation needn't mean one-size-fits-all: Users should always know they're on one of your websites, even if they all look very different. Most importantly of all, they know they won't ever get lost.
14. Link to discussions on the web, don't host them: Only host web-based discussions where there is a clear rationale
