The Polderbaan (18R/36L) east side.
Note: Beware of tightened parking restrictions all around the Polderbaan area! Police strictly enforce them!
The Polderbaan is the newest runway at Schiphol. The runway is in the middle of nowhere (by Dutch standards anyway) and is therefor used heavily as only few people are hindered by noise. Therefor a lot of interesting planes can be seen from here. Best yet is that the viewing possibilities are excellent. On the west side of the runway you can walk along the entire perimeter of the runway with little blocking your view. On the east side of the runway the view is a bit more restricted, but still very good.
The east side of the runway is in particular usefull in the morning, as the sun will be in your back. Early noon the sun will be facing you and you might want to leave for the western side of the runway.
You can get close to the action. For a side-on shot of a 747 no more than 40mm should be used. You could walk into the fields if you have a longer lense, but I would not recommend it. The farmer of the fields is not at all happy with spotters going over his fields and has made that quite clear in the past. Even threatened with violence on more than one occasion (fortunately it never got this far).
Without a car you won’t even have to consider going here. It can not be done without travelling for a long, long time.
From Schiphol plaza you should get onto the A4/E19 motorway in the direction of Den Haag. Exit at the first exit (Hoofddorp / Aalsmeer). At the end of the exit turn to the left onto the N201 (Kruisweg, changes halfway into “Weg om de Noord”) in the direction of Hoofddorp.
Continue following that road. After a few kilometres you will find an exit to the right towards Boesingheliede. Take that exit and turn right at the N520 (Hoofdweg). At the first main crossing turn to the left onto the N232 (Schipholweg).
At this road you should again turn left onto the N519 (IJweg). At the end of this road you will find the runway. Please note that you are no longer allowed to park your car here. The entire IJweg has signs banning parking and from the latter half onwards even stopping! The police enforce the new parking rules very tightly! A parking fine costs roughly 60 euro. The best thing you can do is park in the village of Boesingheliede and walk down to the spot. The walking distance would be a bit less then 1 km.