Up until a couple of years ago, it was a straight forward choice for those parents without plenty of loose change and with children who have not been tortured, er tutored in music:
Boys to FH boys and girls to Sydenham girls.

However there is another fairly serious player now - Kingsdale - in Southwark, just behind Sydenham Hill station. A failing large mixed school, it secured some ?30m(!) as part of the schools for the future programme, and now has an impressive building and an intense and charismatic head. It has no catchment area and indeed the head has made a point this year of visiting primary schools in se23 - they want our children!
The catch is that its exam results, while improving are nothing special and possibly reflect the old intake and old set up rather than the new.

So Kingsdale has no form to go on, but I feel it certainly has given parents something new to consider. I hope I've been fair and accurate as choice of secondary schools is obviously a very sensitive subject.