Declaring a 2D array without knowing its size in C#

I would like to use a 2-D array but I can't know its size in advance. So my question is: how to declare it? And then how to add values into it?

String[,] tabConfig = new String[?, 4];
foreach(blabla with i)
{
    tabConfig[i, 0] = a;
    tabConfig[i, 1] = b;
    tabConfig[i, 2] = c;
    tabConfig[i, 3] = d;
}

I know I can also use a list but I am not very familiar with it.

Thank you!

EDIT: Brace yourselves! Here come my true code with Jon Skeet's help!

List<string[]> tabConfig = new List<string[]>();
String[] temp = new String[4];//The array that will be inside the List
int line = 0, column = 0;

foreach (XmlNode e in doc.DocumentElement.ChildNodes)
{
    if (e.Attributes["Server"].Value == choice)
    {
        temp[0] = e.Attributes["Serveur"].Value;//Here is value 'a'

        column = 1;
        foreach (XmlNode i in e.ChildNodes)
        {
            temp[colonne] = i.InnerText;//Here are values 'b', 'c' and 'd'
            column++;
        }
        tabConfig.Add(temp);//Put a new line into the List
        line++;
    }
}

And to call it:

foreach(string[] array in tabConfig)
    foreach(String txt in array)
        Console.WriteLine(txt);