There is hithergreen.org.uk which also covers Lewisham and bits of Catford and Ladywell.

Brockley Central mainly covers the Hill Fields side and includes Ladywell and New Cross
http://brockleycentral.blogspot.com/

There's also the The Hill which is the Telegraph Hill side of Brockley and includes New Cross
http://www.thehill.org.uk/

There is Downham Online for that area but tends to be full of ole' codgers talking about the 1950's.
http://www.downhamonline.org.uk/