FRA...coming in from the East:
Make sure you sit on the right side of the aircraft, then you'll see:
The skyline of Frankfurt (well maybe not that impressive on an international scale, but the best we have in Germany nonetheless), then you'll have Frankfurt Stadtwald beneath, take a look onto Waldstadion and the Horse Racetrack, then you cross Autobahn A5 and from then on, you're above airport grounds, have a nice look at T2, big birds especially in the morning and in the late afternoon/evening, after touchdown you'll see T1 (basically LH homeground), lots of big birds in blue-yellow and other Star Alliance colours, then the large LH Technik building, then part of Cargo City and in the end, just when the aircraft is about to turn around to get to its parking position, take a look at the aircraft parked out there, CX, QF, TG all park their equipment out there during the morning..with some luck you'll have Wunala dreaming there...
From the West:
You'll cross over River Rhine, have on the right side Opel City in Russelsheim, some smaller lakes with lots of nude girls in the summer
if you can make that out from the aircraft (Kelsterbach Baggersee), then you'll see the infamous Startbahn (Runway) West, maybe some other aircraft about to take off.