Did you know that Goodreads has a quotations database with tens of
thousands of quotations and about 40,000 tags?
http://www.goodreads.com/quotes
Some of them are even (loosely) sourced, although I don't know how
because there's no source field in the new quote form:
http://www.goodreads.com/quotes/new .
I'm wondering if this makes my idea of a Wikiquote profile on Goodreads
(
http://www.goodreads.com/itwikiquote ) useless, and if Goodreads users
may be interested in reading (and editing) Wikiquote.
In that case, you may try to create an English Wikiquote profile: you
can even import books without ISBN, all listed in a CSV spreadsheet with
author and title (or even title only), and they'll look for matching
books automatically.
Nemo