Aggregate String Array

   Public Function AggregateStrings(strings As IEnumerable(Of String), separator As String) As String
        Return strings.Aggregate("", Function(txt As String, current As String)
                                         If Not String.IsNullOrEmpty(txt) Then
                                             Return String.Format("{0}{1}{2}", txt, separator , current)
                                         End If
                                         Return String.Format("{0}", current)
                                     End Function)

    End Function

Usage:

        Dim values As List(Of String) = New List(Of String) From {"100", "200", "300"}
        Dim result As String = AggregateStrings(values, " "c)