Modern Form Tutorials?

Does anyone have a link to a good, modern, tutorial on using forms
other than the form_for helper? Basically, I'm looking for a good How
To on setting up a Ajax form that sits at the bottom of a list members
of a group for adding new users to that group.

You’ll probably want to have a look at this:

The code is fairly straight-forward, and it was written by the guy who introduced the new accepts_nested_attributes_for functionality into rails.