There are various book discussion sites on the Web, some run by book sellers,
others by book enthusiasts. Lately the most useful way I've found for
locating good book discussions is via links from people I follow
on social media. There are also social sites specifically
for sharing information about the books you own,
and connecting with similar book fans. Two of the largest are
LibraryThing and GoodReads.
If you'd like to find or publicize
face-to-face book discussions in your local area,
the Reader's Circle website provides a useful listing service. The American Library Association also has
resources on book discussion groups.
Research and Reference
This site is hosted by the
University of Pennsylvania Libraries,
which have links to many resources for online research.
Some of the resources listed
are not accessible by the general public, but many of them (those marked as "unrestricted access") are open to the world.