Invoicing is something you should have under control. With UctoX, you have everything in one place including an editor which lets you customize the invoice however you want to.
There is an older build available, but please note that it can't be updated and thus I can't provide support for it. This version should only be downloaded by existing customers who need backward compatibility. Note that iCloud or Dropbox synchronization is not recommended in combination with newer version on other devices. http://trial.charliemonroe.net/uctox/UctoX_2_Yosemite.zip
UctoX 2 is a powerful, yet simple-to-use invoicing app - and much more! Unlike other invoicing apps, it also includes features of an accounting app: you can manage your bank statements, cash register, storage, journey log and much more! It comes with 3 built-in print templates, but using the print editor, you can create your own just in a jiffy!
Simplicity - UctoX 2 is designed to be used by the user without too much learning. But if you need any help, there's always a user guide available from the Help menu (OS X) or using the question mark button on main screen (iOS).
IiCloud - sync your accounts via iCloud - between all your devices (iOS and OS X).
Customizable - customize the template for printing invoices, bills and other documents just like you'd like.
Give it a whirl! - download a trial version above and try for yourself!