WPF

<StackPanel>
  <TextBox Text="{Binding MyViewModelList[0]}">
  <TextBox Text="{Binding MyViewModelList[1]}">
  <TextBox Text="{Binding MyViewModelList[2]}">
</StackPanel>

private List<string> _myViewModelList;
       public List<string> MyViewModelList
       {
           get
           {
               return _myViewModelList;
           }
           set
           {
               if (_myViewModelList != value)
               {
                   _myViewModelList = value;
                   RaisePropertyChanged("MyViewModelList");
               }
           }
       }

       private string MouseDown()
       {
           string finalString = "";
           foreach (string str in MyViewModelList)
           {
               finalString += str +", ";
           }
           return finalString;
       }

Matt T Heffron

private const int NumberOfStrings = 3;  // use appropriate number (and better name), your code showed 3
public ViewModel()   // constructor
{
  MyViewModelList = new List<string>(NumberOfStrings);
  for (int i = 0; i < NumberOfStrings; ++i)
  {
    MyViewModelList[i] = string.Empty;
  }
}
public List<string> MyViewModelList { get; private set; }