//Java
import org.apache.wicket.extensions.markup.html.form.select.Select;
import org.apache.wicket.extensions.markup.html.form.select.SelectOption;
...
//variable to hold the selected value from dropdown box,
//and also make "jQuery" selected by default
private String selected = "jQuery";
Select languages = new Select("languages", new PropertyModel<String>(this, "selected"));
form.add(languages);
languages.add(new SelectOption<String>("framework1", new Model<String>("Wicket")));
languages.add(new SelectOption<String>("framework2", new Model<String>("Spring MVC")));
languages.add(new SelectOption<String>("framework3", new Model<String>("JSF 2.0")));
languages.add(new SelectOption<String>("Script1", new Model<String>("jQuery")));
languages.add(new SelectOption<String>("Script2", new Model<String>("prototype")));
//HTML for dropdown box
<select wicket:id="languages">
<optgroup label="Frameworks">
<option wicket:id="framework1" >Wicket (1.4.7)</option>
<option wicket:id="framework2" >Spring MVC (3.0)</option>
<option wicket:id="framework3" >JSF (2.0)</option>
</optgroup>
<optgroup label="JavaScript">
<option wicket:id="Script1" >jQuery (1.6.1)</option>
<option wicket:id="Script2" >prototype (1.7)</option>
</optgroup>
</select>