クリップボードを監視してテキストボックスに追加していく感じの。

gistfile1.cs

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;

internal class MainForm : Form
{
    [DllImport("user32.dll", SetLastError = true)]
    private extern static void AddClipboardFormatListener(IntPtr hwnd);

    [DllImport("user32.dll", SetLastError = true)]
    private extern static void RemoveClipboardFormatListener(IntPtr hwnd);

    private TextBox log;

    public MainForm()
    {
        log = new TextBox
            {
                Dock = DockStyle.Fill,
                Multiline = true
            };
        Controls.Add(log);
    }

    protected override void OnLoad(EventArgs e)
    {
        AddClipboardFormatListener(Handle);
        base.OnLoad(e);
    }

    protected override void Dispose(bool disposing)
    {
        RemoveClipboardFormatListener(Handle);
        base.Dispose(disposing);
    }

    protected override void WndProc(ref Message m)
    {
        if (m.Msg == 0x31D)
        {
            log.Text += Clipboard.GetText() + "\r\n";
            m.Result = IntPtr.Zero;
        }
        else base.WndProc(ref m);
    }
}

internal class Program
{
    [STAThread]
    private static void Main(string[] args)
    {
        Application.EnableVisualStyles();
        Application.Run(new MainForm());
    }
}