Markup Maker is a very convenient way to quickly get a valid (X)HTML structure for web pages you make.
Just paste in your (semantically correct) div ids for the layout you want. Choose if you want inline CSS or a separate file and which Doctype your document should have.
After that simply click on “Convert to XHTML” and you’ll get a nicely formatted HTML & CSS document.
I just received word that this blog’s CSS doesn’t cope very good with Microsoft’s Internet Explorer webbrowser. As the only Computer I own is a Mac I can neither verify this, nor hack the CSS to display properly on this particular browser.