Function to return the closest Date to Today (inclusive) from Ordered list

Because this method is Public you should check if lstOrderedDates is Nothing and you should't believe that the passed List really is ordered.

Doing the check on lstOrderedDates.Count for 0 and 1 first will save one indentation for the meat of the code.

Placing Dim dateToCheck = lstOrderedDates.ElementAt(1) inside the loop will remove the need for the third if inside the loop.

The second if isn't needed at all because of the first if. You can just set selectedDate = dateToCheck.

Would lead to:

Public Shared Function GetClosetDateToToday(lstOrderedDates As List(Of Date)) As Date

    ' Select the closest Delivery date to TODAY (inclusive) from the list of Ordered dates 
    If lstOrderedDates is Nothing OrElse lstOrderedDates.Count = 0 Then
        Return Nothing 
    ElseIf lstOrderedDates.Count = 1
        Return lstOrderedDates.ElementAt(0) 
    End If
    Dim ordered as List(Of DateTime) = lstOrderedDates.OrderByDescending(function(d) d).ToList()
    Dim selectedDate = ordered.ElementAt(0)
    For i = 1 To ordered.Count - 1

        Dim dateToCheck = ordered.ElementAt(i)

        If dateToCheck < Date.Now.Date Then
            Exit For
        End If

        selectedDate = dateToCheck

    Next i
    Return selectedDate

End Function 

In C# I would do it using some Linq magic like so

    public static DateTime GetClosetDateToToday(List<DateTime> ordered)
    {
        if (ordered == null || ordered.Count == 0) { return default(DateTime); }

        var result = ordered
                     .OrderByDescending(item => item)
                     .LastOrDefault(item => item >= DateTime.Now);

        if (result == default(DateTime))
        {
            return ordered[0];
        }
        return result;
    }

which should be equal to the VB.NET version but without guarantee

Public Shared Function GetClosetDateToToday(lstOrderedDates As List(Of Date)) As Date

    ' Select the closest Delivery date to TODAY (inclusive) from the list of Ordered dates 
    If lstOrderedDates is Nothing OrElse lstOrderedDates.Count = 0 Then
        Return Nothing 
    End If

    Dim found as DateTime = lstOrderedDates
                            .OrderByDescending(function(d) d)
                            .LastOrDefault(function(d) d >= DateTime.Now)
    If found is Nothing then
        found = lstOrderedDates.ElementAt(0) 
    End If

    Return found 

End Function