You're able to override the existing RichTextBox toolbar menu selects and buttons or create new ones. The example below overrides and extends (still sets the Font as the current Select does) the existing Font select. Just add your own additional logic and you can do most that you'll require. The Documentation (Start/Programs/RichTextBox v2.0/Documentation) covers these classes and all their members.

In your .aspx.cs or server script -

protected RichTextBoxControl.ToolbarButton toolButton;

protected RichTextBoxControl.ToolbarMenu fontMenu;

private void Page_Load(object sender, System.EventArgs e)

 {

     fontMenu = new RichTextBoxControl.ToolbarMenu("FontMenu", true);

     RichTextBoxControl.ToolbarMenuItem item = new  

     RichTextBoxControl.ToolbarMenuItem();

     item.Name = "Tahoma"; 

     item.Value = "Tahoma";

     fontMenu.Items.Add(item);

     item = new RichTextBoxControl.ToolbarMenuItem();

     item.Name = "Arial"; 

     item.Value = "Arial";

     fontMenu.Items.Add(item);

     fontMenu.OnChange = "myMenuHandler";

     fontMenu.Title = "Font";

     this.RichTextBox1.CreateToolbarMenu(fontMenu);

 }

In your client script of your .aspx page -

<script language="javascript" type="text/javascript">

  function myMenuHandler(editor,isHtmlMode,text,value)

  {

      //the following 3 lines are from the existing function

      if (isHtmlMode) return;

      editor.focus();

      editor.document.execCommand('fontname','',value);

      //add you additional logic here to extend the code fired above

   }

</script>

Or with an existing toolbar button -

 protected RichTextBoxControl.ToolbarButton toolButton;

 toolButton = new RichTextBoxControl.ToolbarButton("Print", true);

 toolButton.ClientOnClickFunction = "myButtonHandler";

 this.RichTextBox1.CreateToolbarButton(toolButton);

In your client script of your .aspx page -

<script language="javascript" type="text/javascript">

  function myButtonHandler(editor, isHtmlMode)

  {

       alert('print');

  }

</script>

To create a new toolbar button the code would be like the following -

toolButton = new RichTextBoxControl.ToolbarButton("NewButton", false); 

You'd then add new .gif files to the appropriate images directory called NewButton.gif and NewButton_over.gif so that these are picked up in the render of the new image button.