Five XHTML Elements You Didn't Know But Were Afraid to Ask

Here are some important XHTML tags that are rarely used by web developers

Five XHTML Elements You Didn't Know But Were Afraid to Ask by Adam Tibi

Nice short article about the use of optgroup, label, fieldset/legend, col/colgroup and acronym tags, with screenshots of what they look like.

I especially like the optgroup one, very useful, the fieldset I have been using for a while and makes grouping controls much more intuitive.