wkhtmltopdf is a superb tool that can be used to convert a given url or local html page, to pdf format. This tool after installing can be embeded inside php code,inside shell script or any other scripting language.
there are several web based online tools available wherein you can specify the URL you need to convert to pdf as input and download the converted pdf file as output.
But those tools cannot be used while working in a console terminal, or is not a viable option when you need that functionality in a script.
wkhtml to pdf uses webkit engine and qt for converting html to pdf. this package is available for downloaded from googlecode.com
We tested this on an ubuntu machine...(works well with Red hat based machines also).