A Clearer Understanding of (X)HTML Forms
The Web Standards Project has some very useful, and sometimes quite entertaining, tutorials setting readers straight on some important topics that you may think you have already mastered, such as (X)HTML forms. Their forms tutorials explain beginner, intermediate, and advanced techniques with a focus on accessibility. Of course they also talk a bit about how CSS can be used to layout and format your forms so they can be as beautiful as they are Accessible. The advanced tutorial talks about the :focus pseudo element, which works in Mozilla browsers and can be used to alter the style of a form element when the user tabs to the element or clicks inside it.
If you are not familiar with label, fieldset, legend, and optgroup then these tutorials are for you.