public class Item
{
 public Item(string term, int freq)
 {
  _term = term;
  _freq = freq;
 }

 private string _term;
 public string Term
 {
  get { return _term; }
  set { _term = value; }
 }

  private int _freq;
  public int Freq
  {
   get { return _freq; }
   set { _freq = value; }
  }
 }

 public class ItemComparer:IComparer<Item>
 {
  #region IComparer<Item> Members

  public int Compare(Item x, Item y)
  {
   return y.Freq - x.Freq; //descending sort
   //return x.Freq - y.Freq; //ascending sort
  }

  #endregion
 }

static void Main()
{
 List<Item> items = new List<Item>();
 ....
 items.Sort(new ItemComparer());
}