Stunning design doesn't really come from having "beautiful" html code so much I feel. People who really get design are the ones who think about how a product is going to be used, who is using it, and in what context. If you are talking strictly visual design, then the CSS/HTML markup is going to be even less relevant. For that I would go to CSS sites and galleries and derive inspiration from there.
Oh I agree. We inspect elements of beautiful sites in Firebug to answer the question "How was that specific thing made?" Obviously Firebug does not find inspiration for you, it won't teach you the principles of design and it isn't going to design sites for you.
