IntPtr nextClipboardViewer;

public Form1()
{
    InitializeComponent();
    nextClipboardViewer = (IntPtr)SetClipboardViewer((int)
                this.Handle);
}
[DllImport("User32.dll")]
  protected static extern int
            SetClipboardViewer(int hWndNewViewer);
[DllImport("User32.dll", CharSet=CharSet.Auto)]
public static extern bool
         ChangeClipboardChain(IntPtr hWndRemove,
                              IntPtr hWndNewNext);
[DllImport("user32.dll", CharSet=CharSet.Auto)]
public static extern int SendMessage(IntPtr hwnd, 
                                     int wMsg,
                                     IntPtr wParam,
                                     IntPtr lParam);

protected override void WndProc(ref System.Windows.Forms.Message m)
{              
    const int WM_DRAWCLIPBOARD = 0x308;
    const int WM_CHANGECBCHAIN = 0x030D;

    switch (m.Msg)
    {
        case WM_DRAWCLIPBOARD:
            DisplayClipboardData();
            SendMessage(nextClipboardViewer, m.Msg, m.WParam,
                        m.LParam);
            break;

        case WM_CHANGECBCHAIN:
            if (m.WParam == nextClipboardViewer)
                nextClipboardViewer = m.LParam;
            else
                SendMessage(nextClipboardViewer, m.Msg, m.WParam,
                            m.LParam);
            break;

        default:
            base.WndProc(ref m);
            break;
    }
}

void DisplayClipboardData()
{
    try
    {
        IDataObject iData = new DataObject();
        iData = Clipboard.GetDataObject();

        if (iData.GetDataPresent(DataFormats.Rtf))
            richTextBox1.Rtf = (string)iData.GetData(DataFormats.Rtf);
        else if (iData.GetDataPresent(DataFormats.Text))
            richTextBox1.Text = (string)iData.GetData(DataFormats.Text);
        else
            richTextBox1.Text = "[Clipboard data is not RTF or ASCII Text]";
    }
    catch (Exception e)
    {
        MessageBox.Show(e.ToString());
    }
}

protected override void Dispose(bool disposing)
{    
    if (disposing)
    {
        if (components != null)
        {
            components.Dispose();
        }
    }
    base.Dispose(disposing);
}

protected override void Dispose(bool disposing)
{
    ChangeClipboardChain(this.Handle, nextClipboardViewer);
    if (disposing)
    {
        if (components != null)
        {
            components.Dispose();
        }
    }
    base.Dispose(disposing);
}