SplitButton

Sample Ribbon XML file:

<customUI xmlns="http://schemas.microsoft.com/office/2006/01/customui">
   <ribbon startFromScratch="false">
       <tabs>
          <tab id="MyTab" label="My Tab">
             <group id="MyGroup" label="Sample Split button">
               <splitButton id="mySplitButton" 
                            size="large">
                   <button id="myButton1" imageMso="HappyFace"
                     label="Click me" onAction="MyButton1CallbackOnAction"/>
                      <menu id="mySplitMenu" itemSize="large">
                         <button id="myButton2" imageMso="TableStyleRowHeaders"
                           label="Point 1."
                           onAction="MyButton2CallbackOnAction"
                           description="The 1st Point"/>
                         <button id="myButton3" imageMso="TableStyleColumnHeaders"
                           label="Point 2."
                           onAction="MyButton3CallbackOnAction"
                           description="The 2nd Point"/>
                         <button id="myButton4" imageMso="TableStyleLastColumn"
                            label="Point 3."
                           onAction="MyButton4CallbackOnAction"
                           description="The 3rd Point"/>
                      </menu>
                </splitButton>
             </group>
         </tab>
      </tabs>
   </ribbon>
</customUI>

The SplitButton requires either a <button> or <toggleButton> control. Furthermore a <menu> control is required for the SplittButton menu. 

Attributes: enabled, id, idMso, idQ, insertAfterMso, insertAfterQ,
                 insertBeforeMso, insertBeforeQ, keytip, label, screentip,
                 showLabel, size, supertip, tag, visible

Callbacks: getEnabled, getKeytip, getShowLabel, getSize,
                  getSupertip,  getVisible

You can find this sample in Sample DB 1