I used wkhtmltopdf in a previous project and found it to be extremely reliable and easy to use. I was extracting the HTML mime parts from incoming email, converting them to PDFs with wkhtmltopdf, then converting that to a PNG with ImageMagick and displaying the PNG to the user in a web browser.
Originally because I didn't find a free app which would do that. Then I decided to keep the PDF as it was quite useful. Unlike with the PNG, the HTML links were retained in the PDF. Ie, HTML anchor tags are still clickable in PDFs generated by wkhtmltopdf.
EDIT: A PDF will also let you select text, unlike an image. However, an image is nicer to embed in a webpage. So I utilised both in order to get the best of both worlds.
Oops just noticed this comment. See my other comment (wkhtmltoimage is part of the package, allows you to render HTML+CSS into PNG, compile into x64 and place binary in your git repo directory to use on heroku)
