PDFShift - Convert any HTML documents to high-fidelity PDF using a single POST request
pdflayer - Free, powerful HTML to PDF API supporting both URL and raw HTML conversion. Unlimited document size, lightning-fast and compatible PHP, Python, Ruby, etc.
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.
Tcpdf - TCPDF: Open Source PHP Class for generating PDF documents
HTML2PDF.fr - HTML2PDF is a HTML to PDF converter that allows the conversion of valid HTML 4.