I think its London Metropolitan Archives
Yes, that's right. They hold the church records of most of the London churches. Ancestry are busy digitising them, and they will be available soon. A must, if you have ancestors in or around London.
Ancestry already have many of the Poor Law Union records online, and the Criminal Registers for England and Wales 1791-1892, Thacker's Indian Registers, and The East India Register and Directory. Access to these has to be via "Enhanced" membership or better, I believe (I'm on the World Membership, so I get them all).
I can't answer corb66's second question, I'm afraid. My only experience with FindMyPast was in the early days of my research, when I bought some credits from them, and I've also used them for the 1911 census, and I wasn't at all impressed at the way they handled that.