The viewing spots I have currently heard of are:
*Sheldon Country Park: Good view of planes landing on 15 and taking off from 33 quite low.
*Aviation Centre: There is a good view of the entire runway with a clear window.
*Terminal 1: There are dots on the window which could be distracting but the view isn't that bad once you don't pay attention to them. Back in July (2010) this window was cut off due to works on merging Terminal 1 and 2 together, and a possible new terminal.
*Long Stay Car Park: Good for close-ups of 15 departures, 33 arrivals, planes vacating off 15 and taxiing to 33.
If there are any I missed out please post them.