Depends on what you are aiming to output. Plain text monospaced output? There are always Perl formats ...

Arrowhead touched on troff. It's a good lightweight system, with excellent typographic control. The excellent tutorial book Unix Text Processing is available for free download from http://www.alltel.net/~kollar/utp/.

You might want to look at PDF. If you need to create simple PDFs from scratch, PDFlib is your (admittedly low -level) friend.

If you are getting forms in as PDF blanks (it happens), I've seen clever things demonstrated with PDF::API2.

Most workflows accept PDF as a native file format. Good luck!