PDFShift - Convert any HTML documents to high-fidelity PDF using a single POST request
PDFreactor - PDFreactor is a cross-platform enterprise-grade HTML to PDF conversion engine.
PDFCrowd - Pdfcrowd is a Web/HTML to PDF online service. Convert HTML to PDF online in the browser or in your PHP, Python, Ruby, .NET, Java apps via the REST API.
PDFSwitch - Convert any HTML document or URL to PDF with a single API request.
HTML2PDF.fr - HTML2PDF is a HTML to PDF converter that allows the conversion of valid HTML 4.
Tcpdf - TCPDF: Open Source PHP Class for generating PDF documents