New to rails and I'm working on a site for ebooks and was wondering if
there are any plugins for rails that will allow me to generate pdfs on
the fly like safari books, where after you order a book it prepares a
pdf with your user name on each page.
No, there aren't, but you can use the pdfstamp.pl from Perl's Text::PDF to do it. That's what I use for my ebook on building e-commerce sites in Rails.