OCLC's Worldcat has begun a new service showing the most important
bibliographic information about any author - the identities series. Here is
the entry for Twain showing the books by and about him from the beginning:

http://orlabs.oclc.org/identities/lccn-n79-21164

I've also just learned this week that as a part of the settlement with the
publishers and authors, Google Books will allow every public and university
library in America to have one machine that can access about 5 million books
that are in copyright but out of print.
What an age.