This is a modified version of an Excel service invoice template that was uploaded to docstoc by someone at Oregon Health and Science University. That template had some problems including having embedded images from Oregon Health and Science University that were hard to get rid of. I've tweaked it just a bit to serve my needs.
I like to send my invoices in the body of emails I send to my clients and I discovered that if you save the .xls file as a web page, not only is the resulting .htm file fully editable and savable within Excel, you can also copy the cells to your clipboard and paste them into an Outlook Express email and it looks nice. When you save the .xls file as a web page, Excel will create the .htm file and a corresponding folder holding extra information. After saving this way, the page that you will be seeing in Excel for editing will the .htm version. This is the version to copy and paste from if inserting the invoice into an html styled email message.
The quantity column can be hours or pieces. If you want pieces, best to format the cells for no decimal places.
I have a set hourly fee, so I used Excel's "fill" feature to pre-populate the Rate column, however you can rename that column "unit Price" or whatever suits you and either pre-populate it or enter individual values in each cell on the fly.
I bill per day, hence the date column on the left. If you don't want it, just delete that column.
Have fun and don't work too hard.
Farmrchrys