public static List<DateTime> NextDays(this DateTime actual, int daysAhead, List<DateTime> list = null)
{
    if (list == null)
        list = new List<DateTime>();

    list.Add(actual);

    if (daysAhead == 0)
        return list;

    if (daysAhead > 0)
        return NextDays(actual.AddDays(1), --daysAhead, list);

    return NextDays(actual.AddDays(-1), ++daysAhead, list);
}

public static List<DateTime> NextWeekDays(this DateTime actual, int daysAhead, List<DateTime> list = null, bool? backwards = null)
{
    if (list == null)
        list = new List<DateTime>();
    if (backwards == null)
        backwards = daysAhead < 0;

    if (actual.DayOfWeek == DayOfWeek.Saturday)
        actual = actual.AddDays(backwards.Value ? -1 : 2);
    else if (actual.DayOfWeek == DayOfWeek.Sunday)
        actual = actual.AddDays(backwards.Value ? -2 : 1);

    list.Add(actual);

    if (daysAhead == 0)
        return list;

    if (daysAhead > 0)
        return NextWeekDays(actual.AddDays(1), --daysAhead, list, backwards);

    return NextWeekDays(actual.AddDays(-1), ++daysAhead, list, backwards);
}