On Terminal 1, there are two viewing areas located on the upper level. Both, located at both extreme sides of the terminal, are indoor with glass windows. One overlooks the domestic area plus the Terminal 2. The other, on the right end, lets you look at international aircraft parked on the jetways below. Both provide great views of taxing aircraft and one of the main runways behind. On the same level there is a cafeteria/restaurant that also provides windows for spotting, located in the middle of the two viewing galleries.
I don´t know if Terminal 2 has a viewing area.