The URL is http://www.csszengarden.com/, and it's my favorite because it shows what users can do with a single CSS stylesheet, and how people have their own approach to designing a website.
No, the home page does not validate.
Yes, the second page does vaildate.
The first page has 4 validation errors.
The home page of the website would get an 9 out of 10. The style chosen to write the homepage in is very calming, and everything looks clean and organized. All resources needed are provided, and the article on the main page is straight to the point.
The usability of the website gets a 10 out of 10; again, everything that a user would need to browse the site is available, as well as any and all relevant information.
The site meets its purpose, to show users that there is infinite possibilities with a singular CSS file, and to show people what others have already created.