.neT: HTML select tag with groups

<form action="example.php">
<div>
<select>
<optgroup label="Server-side languages">
<option>PHP</option>
<option>ASP</option>
</optgroup>
<optgroup label="Client-side languages">
<option>JavaScript</option>
<option>VBScript</option>
</optgroup>
</select>
</div>
</form>

http://www.htmlquick.com/reference/tags/select.html