http://www.boxbilling.com/en/ I just found this today, and thought it was pretty interesting for hosts.
It's good, but I tried it and get 500 errors everytime and can't get it to work again. Plus the amount of files they use is outrageous, but it's still nice.
I might give it a try. I have been looking for a nice billing script for a while so I will see if I can get it to work