[simonsarris]

The library that I make, GoJS (http://www.gojs.net/) has a tree layout and layered digraph layout, both with many options.

Here's an overview of the options for the layered digraph layout: http://www.gojs.net/latest/samples/ldLayout.html

The tree layout supports some fairly complicated tree structures, including ones that alternate or have different configurations for leaves: http://www.gojs.net/latest/samples/tLayout.html

Disclosure: I'm a developer of this library and it is not free.

[davidjgraph]

Also commercial with digraph layout functionality:

http://www.lassalle.com/

http://www.jgraph.com/

http://www.tensegrity-software.com/category/javascript-html5...

http://www.yworks.com/en/products_yfileshtml_about.html