Prawn is pretty neat, but what I'd really like to see is HTML to PDF in pure Ruby. I had to use a Java library wrapped in a Ruby module to do this. Complicates my server configuration (needs the JVM) more than I'd like.
I'm the maintainer of Prawn, and yeah, it'd be nice to see this. Jamis Buck tried this with prawn-format, but after a while we dropped support for it because it fell behind our core library and started breaking (Jamis had since moved on to other things).
In order for this to happen, what we really need is a solid box model. Since we don't have that yet, it's a very hard problem. If someone wanted to pay me to work on it full time for a year, I could get it built.
But failing that, we'll have to wait a good deal of time for this, unless someone else finds a large chunk of dedicated time for it.
Until then, Flying Saucer is the way to go if you can't afford PrinceXML price tag.
You can try HTMLDOC (http://htmldoc.rubyforge.org/) which is a wrapper around a C library (I believe) that does exactly this. I've used it before, it's pretty fast and stable and you don't have to worry about JVM.
