There's no deck unfortunately, but plenty of places with views. From the car-park next to the terminal you can easily see things on the rwy but it's not great for photography. To the west of the terminal (Canary Wharf end) you can get line-up/landing shots by the threshold. Going past the terminal/car-park you can stop in an area adjacent to the threshold for the westerly rwy...got some good t/o shots from here too. There are probably other places but those are the best I've found. Don't forget that the place closes between 1200 Sat and 1200 Sun, but it's far busier during the week anyway.
Biggidy biggidy bong