One of the interesting features in Editing is the speller and it works really well. :) One of the ineteresting scenarios when it comes to speller is to add the speller choices to a custom context menu. The speller choices would have to be added in the ContextMenuOpening event handler as below:

 
spellingError = textBox.GetSpellingError(caretIndex); 
if (spellingError != null)
{
   foreach (string str in spellingError.Suggestions)
   {
      MenuItem mi = new MenuItem();
      mi.Header = str;
      mi.FontWeight = FontWeights.Bold;
      mi.Command = EditingCommands.CorrectSpellingError;
      mi.CommandParameter = str;
      mi.CommandTarget = textBox;
      textBox.ContextMenu.Items.Insert(cmdIndex, mi);
      cmdIndex++;
   }
   Separator separatorMenuItem1 = new Separator();
   textBox.ContextMenu.Items.Insert(cmdIndex, separatorMenuItem1);
   cmdIndex++;
   MenuItem ignoreAllMI = new MenuItem();
   ignoreAllMI.Header = "Ignore All";
   ignoreAllMI.Command = EditingCommands.IgnoreSpellingError;
   ignoreAllMI.CommandTarget = textBox;
   textBox.ContextMenu.Items.Insert(cmdIndex, ignoreAllMI);
   cmdIndex++;
   Separator separatorMenuItem2 = new Separator();
   textBox.ContextMenu.Items.Insert(cmdIndex, separatorMenuItem2);
}
 
 

Thats all there is to it. Its the same for RichTextBox except for the first line where you get the spellingError - rtb.GetSpellingError(rtb.CaretPosition)

The complete sample code is attached so that you can see it working in all glory :)..