I love the idea of Mike Stenhouse's CSS Framework. It's so simple: name the elements in your XHTML with a specific set of names, and then create your CSS to match that. The only problem with this framework is I haven't seen any good-looking designs on top of it. For good-looking design examples, see the CSS Zen Garden or Open Source Web Design.
While the CSS Zen Garden is nice, most of the designs are not useable for web applications. They're more of a showcase of what CSS can do, and often contain too many images for a real-world application or website. The designs from oswd.org, on the other hand, are perfect for web applications. However, the underlying HTML is different for each design.
So how do we marry the two? Maybe we should lobby some designers at oswd.org to use the CSS Framework for their designs? I think this would be a great asset to many communities - imagine what you could do with your Drupal theme if you didn't have to change your template files (only CSS). That'd be pretty cool.