Beauty is in the eye of the beholder. What may be an absolutely beautiful website to you, I might find completely unpleasant. Most of it depends on your topic and your audience.
There are some basic rules that all of us follow about balance on page content, font distribution, image balance, color balance, contrast, etc and there are many books on how those types of pages are laid out.
But to design a beautiful web site is to design a page that your viewers find beautiful. If I had a target audience of Country Music fans there idea of a beautiful website would be far different than a target audience of punk rockers. Both sites might be excellent in their layout, images, colors and contrast but I would be willing to bet that the audiences would not like the others site just based on subject.
Remember designing a site and a page is an artistic process.