There is one on T2 if you don't have a car, but it's only really good from about 16:00 onwards. That said, you can create your own angles if you're lucky.
If you don't mind walking there's a place at Zeppelinheim, about 30 minutes from the terminals, but they must be using the 25s for the place to be any good. There is a bus that goes to the runway 18 deck at the 07 end but I don't have any further details.
You don't have to walk, there's train at Zepplinheim which connects Frankfurt main station, it's S7. From airport, you can take S8 or S9 to Frankfurt Stadion, then interchange S7. From Zepplinheim Station, it's only 600 meters to the viewing spot at rwy 25, a good place for 25L landing and 07C take-off