FOP - XSL-FO to PDF converter. A part of Apache's XML project [Open Source, BSD-like]. - http://xmlgraphics.apache.org/fop/
Xinc - A Java XSL-FO viewer and PDF generator. - http://lunasil.com/
Big Faceless Report Generator - Java Report Writer to convert XML to PDF. Creates dynamic reports with JSPs and Servlets. Features include encryption, bar codes, graphs and charts, custom fonts, Unicode support. [Commercial w/ Evaluation] - http://big.faceless.org/products/report/
Antenna House XSL Formatter - XSL formatting engine that conforms to XSL W3C recommendation. [Commercial] - http://www.antennahouse.com/