//In ctor
{
            this.lb = new System.Windows.Forms.ListBox();
            lb.Items.Add(new ListItem(1, "Test"));
            lb.SelectedIndexChanged += new EventHandler(lb_SelectedIndexChanged);
            this.Controls.Add(lb);
}

        void lb_SelectedIndexChanged(object sender, EventArgs e)
        {
            ListItem item = (ListItem) lb.SelectedItem;
            MessageBox.Show(item.Value.ToString());
        }


public class ListItem
{
    public readonly object Value;
    public readonly string Display;

    public ListItem(object value, string display) {
        this.Value = value;
        this.Display = display;
    }

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