Add Department as a pre-set field on main sales invoice creation screen! You could give your end-user the option to show or hide it, as well. AND - Being able to move the columns around for more customized layout would be nice, too.
I have a client with multiple departments, and I have to add Department to every single transaction line. It sure would be nice to be able to just tab over to that field, versus having to stop typing, grab my mouse, and manually click the three-do...