List<DateTime> list = new List<DateTime>();
list.Add(DateTime.Now);
list.Add(DateTime.Now.AddDays(2));
list.Add(DateTime.Now.AddDays(1));
list.Add(DateTime.Now.AddDays(3));
var list2 = list.OrderByDescending(x => x).ToList();
foreach (var item in list2)
{
Response.Write(item.ToString() + "<BR>");
}