How to sort depended objects by dependency

I merged DMM's idea with the depth-first-search algorithm on Wikipedia. It works perfect for what I needed.

public static class TopologicalSorter
{
public static List<string> LastCyclicOrder = new List<string>(); //used to see what caused the cycle

sealed class ItemTag
{
  public enum SortTag
  {
    NotMarked,
    TempMarked,
    Marked
  }

  public string Item { get; set; }
  public SortTag Tag { get; set; }

  public ItemTag(string item)
  {
    Item = item;
    Tag = SortTag.NotMarked;
  }
}

public static IEnumerable<string> TSort(this IEnumerable<string> source, Func<string, IEnumerable<string>> dependencies)
{
  TopologicalSorter.LastCyclicOrder.Clear();

  List<ItemTag> allNodes = new List<ItemTag>();
  HashSet<string> sorted = new HashSet<string>(StringComparer.OrdinalIgnoreCase);

  foreach (string item in source)
  {
    if (!allNodes.Where(n => string.Equals(n.Item, item, StringComparison.OrdinalIgnoreCase)).Any())
    {
      allNodes.Add(new ItemTag(item)); //don't insert duplicates
    }
    foreach (string dep in dependencies(item))
    {
      if (allNodes.Where(n => string.Equals(n.Item, dep, StringComparison.OrdinalIgnoreCase)).Any()) continue; //don't insert duplicates
      allNodes.Add(new ItemTag(dep));
    }
  }

  foreach (ItemTag tag in allNodes)
  {
    Visit(tag, allNodes, dependencies, sorted);
  }

  return sorted;
}

static void Visit(ItemTag tag, List<ItemTag> allNodes, Func<string, IEnumerable<string>> dependencies, HashSet<string> sorted)
{
  if (tag.Tag == ItemTag.SortTag.TempMarked)
  {
    throw new GraphIsCyclicException();
  }
  else if (tag.Tag == ItemTag.SortTag.NotMarked)
  {
    tag.Tag = ItemTag.SortTag.TempMarked;
    LastCyclicOrder.Add(tag.Item);

    foreach (ItemTag dep in dependencies(tag.Item).Select(s => allNodes.Where(t => string.Equals(s, t.Item, StringComparison.OrdinalIgnoreCase)).First())) //ge