This is something that I had worked on a month or so ago and now have been using these invoices for our company.
http://triton.networkoperations.us/invoice.jpg
Had to spruce it up a bit from its old look.
What I was wondering is if there are already several templates that look like that or better. Because I had to modify PHP Code & Much Much more inorder to get this to work they wa I wanted.
If not then I was going to release a ZIP file with a README in there on how to install this template or if you want you can install it and change it to your specs.
UPDATE:
Download it here