Another vote for seat spy. It is not necessarily fully up to date, usually a lag of a couple of hours. For example, I booked an F reward about 1 hour ago and it's still there. Guess in a couple of hours it will disappear off the system as the data comes through the API.

I have also found seats.aero to be very handy for spotting rewards on non-BA routes. This was most useful when bagging seats from SFO-HND and NRT-CGK.