I have now added trackback pinging to my blog.
As per usual with blog standards there are a number to choose from. I have chosen to use the MoveableType standard even though my site is not produced with it. As so many sites do use it any standard it supports will be fairly widely supported. The spec can be found at http://www.movabletype.org/docs/mttrackback.html
I also considered using the CommentAPI http://wellformedweb.org/story/9. Maybe I will get to that later