WrappingEnumerator

public static class ListEx
{
    public static IEnumerable<T> WrappingEnumerator<T>(this List<T> list)
    {
        var i = 0;
        while (true)
        {
            yield return list[i];
            i = (i < (list.Count - 1))
                    ? i + 1
                    : 0;
        }
    }
}