HTML2PDF is a PHP class using FPDF for the PHP4 release, and TCPDF for the PHP5 release. It can convert valid HTML and xHTML to PDF. More details and examples on http://html2pdf.fr/
HTML2PDF is now on GitHub : https://github.com/spipu/html2pdf/
Reporting engine library written in C. Create one XML file and generate PDF, HTML, TXT, and CSV reports based on queries. Has support for MySQL, PostgreSQL, ODBC. Bindings for PHP, Java, Python.
dompdf - the PHP 5 HTML to PDF converter. dompdf is a (mostly) CSS compliant HTML rendering engine written in PHP. It supports external stylesheets, inline style tags, and the style attributes of individual HTML elements. Requires PHP 5.