I'm fiddling with Black Sheep Invoices right now, which is great at first but now I'm having trouble actually getting it to render the PDFs. Lots of installation difficulties--probably a lot easier on your own server but i'm up on a shared host with it. The HTML output and data management portions are well done though, which is something you won't get out of just creating a postscript template. I was hoping to find a reference to a library that has an active development team though (Black Sheep is not being updated at this time).
