Itemized List of Services _ must be specific People want to know what they've paid for. Most people will not pay for something described merely as "Design." Tell them exactly what they have received: e.g. "Design of three_page static website for Sporting Goods Department." Be as specific as possible. In five years, would both you and the client know what you meant by your description? Also, specify whether the charge is project_based or hourly.
If you are permitted to submit your invoice via email then it is useful to convert the invoice into PDF format so that it cannot be altered. There is a free PDF creator which you can use at PDFCreator. This creates a PDF file from any application which can then be emailed to the client. Better off, if you can use a software system, it will automatically generate invoice in PFD format, you can also email it straight away from within the a software program.