Module Program

    Async Function Main(args As String()) As Task
        Dim count = 100
        Dim url = "foo.bar.baz"
        Dim tasks As New List(Of Task(Of String))

        For i = 0 To count - 1
            tasks.Add(DoRequest(url))
        Next

        Dim whenAll = Task.WhenAll(tasks)
        Dim results = Await whenAll

        ' В results у нас массив результатов всех запросов
        For Each r In results
            Console.WriteLine(r)
        Next
    End Function

    Async Function DoRequest(url As String) As Task(Of String)
        Dim webRequest = HttpWebRequest.Create(url)
        Using response = Await webRequest.GetResponseAsync()
            Using stream = response.GetResponseStream()
                Using reader = New StreamReader(stream)
                    ' Здесь можно сделать что-то с результатом отдельного запроса
                    Return Await reader.ReadToEndAsync()
                End Using
            End Using
        End Using
    End Function

End Module

Module Program

    Sub Main(args As String())
        Dim count = 100
        Dim url = "foo.bar.baz"
        Dim tasks As New List(Of Task)

        For i = 0 To count - 1
            tasks.Add(DoRequest(url))
        Next

        Dim whenAll = Task.WhenAll(tasks)
        whenAll.Wait()
    End Function

    Async Function DoRequest(url As String) As Task
        Dim webRequest = HttpWebRequest.Create(url)
        Using response = Await webRequest.GetResponseAsync()
            Using stream = response.GetResponseStream()
                Using reader = New StreamReader(stream)
                    Dim result = Await reader.ReadToEndAsync()
                    ' Запускаем обработку результата запроса
                    Await Task.Run(Sub
                        HandleRequestResult(result)
                    End Sub)
                End Using
            End Using
        End Using
    End Function

    Sub HandleRequestResult(result As String)
        ' Здесь какая-нибудь долгая обработка запроса
    End Function
End Module