Based on Lance Larsen answer - here's an extension method with the recommended string.Compare instead of string.Equals
It is highly recommended that you use an overload of String.Compare that takes a StringComparison parameter. Not only do these overloads allow you to define the exact comparison behavior you intended, using them will also make your code more readable for other developers. [Josh Free @ BCL Team Blog]
public static bool Contains(this List<string> source, string toCheck, StringComparison comp)
{
return
source != null &&
!string.IsNullOrEmpty(toCheck) &&
source.Any(x => string.Compare(x, toCheck, comp) == 0);
}