This question is not that easy to answer as the leg space is very different depending on plane, airline and therefore route.
Anyhow I didn't found any leg space database/comparison on the web till now. But there is another indicator you can use which is mostly up to date - the seat pitch.
Seat Pitch: The distance between two rows of seats, this is the best indicator of legroom. More is better.
On a quick look, it is mostly United, KLM, Delta, AA on their long-haul Eco Flights. But make sure that you check the aircraft model too.
You should take a look at http://www.seatguru.com/charts/longhaul_economy.php#chart