My large invoice is very similar (well, ok, identical) to the one that PoleMan posted the link to.
I've numptyized it to suit my own needs, letterheading and so on, but for the big jobs, the ones you have to send in invoice in for its perfect.
I use a little invoice for my shops and places that pay up on the nail, or for domestic stuff that are not in, but that is one I made up myself using a spreadsheet.
6 to a page of A4 paper.
With the shops I do, all the shops are already named & priced and all I do is change the date on the first one, then all the dates change on all the others relevent for that day, print them out and then use the guillotine to slice up 5 pages of invoices at a time, perfect

Or a whole load of blanks.
Ian