Hey

You might no this one but here I will officially post the url for it

WWW.phpmanager.com
a script that provides webhost's with an order form,auto account creation, recurring invoicing, built in tech support ticket system and a few other features. it's a decent script.
(I am using this script)

Of course you know of

www.nixt.org


those are the two I know about.

Although their is another one called WHM which comes with Cpanel and

not sure if this is what you want but look at
http://www.webhostingbilling.com