C#

class ComboBoxEx : ComboBox
{
  public ComboBoxEx()
  {
    DrawMode = DrawMode.OwnerDrawFixed;
  }


  protected override void OnDrawItem(DrawItemEventArgs ea)
  {
    ea.DrawBackground();
    ea.DrawFocusRectangle();

    Rectangle bounds = ea.Bounds;
    bool enableItem = false;
    if (ea.Index != -1)
    {
      enableItem = ((ComboBoxExItem)this.Items[ea.Index]).Enabled;
    }

    Font myFont = new Font(ea.Font, FontStyle.Italic);
    if (ea.Index != -1)
    {
      if (enableItem)
      {
        ea.Graphics.DrawString(Items[ea.Index].ToString(), ea.Font, new SolidBrush(Color.Black), bounds.Left, bounds.Top);
      }
      else
      {
        ea.Graphics.DrawString(Items[ea.Index].ToString(), ea.Font, new SolidBrush(Color.Gray), bounds.Left, bounds.Top);
      }
    }
    else
    {
      ea.Graphics.DrawString(Text, ea.Font, new SolidBrush(Color.Gray), bounds.Left, bounds.Top);
    }
    base.OnDrawItem(ea);
  }
}

class ComboBoxExItem
{
  private string _text;
  public string Text
  {
    get { return _text; }
    set { _text = value; }
  }

  private bool _enabled;
  public bool Enabled
  {
    get { return _enabled; }
    set { _enabled = value; }
  }

  public ComboBoxExItem()
    : this("")
  {
  }

  public ComboBoxExItem(string text)
    : this(text, false)
  {
  }

  public ComboBoxExItem(string text, bool enabled)
  {
    _text = text;
    _enabled = enabled;
  }

  public override string ToString()
  {
    return _text;
  }
}