OpenOffice: an open source office suite with built-in PDF creation.
tex2pdf (formerly lyx2pdf) is a script that generates a PDF document from a LaTeX or LyX document using pdf(la)tex, hyperref and other tools. There is a bash shell and Perl implementation available. The bash port (tex2pdf 2.x) is no longer maintained and is considered deprecated. However, you can still find it in the download area of released versions. tex2pdf is coded in Perl from version 3.0 on.
The ReportLab Toolkit is the time-proven, ultra-robust open-source engine for programatically creating PDF documents and forms the foundation of RML; it also contains a library for creating platform-independent vector graphics. It's a fast, flexible, cross platform solution written in Python.
The Panda PDF Generator is intended to make PDFs on the fly for the Web, but may be used to generate any PDF document you want.