The best I’ve seen so far is Prawn:
- Prawn http://prawn.majesticseacreature.com/
- http://advent2008.hackruby.com/past/2008/12/17/awn_and_the_future_of_ruby_pdf_generation/
- http://railstips.org/2008/10/14/how-to-generate-pdfs-in-rails-with-prawn
- Prawn Rails plugin: http://www.cracklabs.com/prawnto