It is well known that there are serious problems with the search
function and the metadata of Google Book Search. My question to Book
People is: Which other ways do you know to find Google Books?

I recently found that U of Indiana library has 3500+ GBS titles in its catalog.

http://www.iucat.iu.edu/

We have already discussed here on UMich's MBooks program. See also:
http://archiv.twoday.net/stories/3425505/

Private link lists

http://pdbooks.zuhause.org/
very large!

Harvesting Google Print
http://homepage.ntlworld.com/jenjonliz/jon/tia/google.html

GOOPFIC collection
http://steinbeck.ucs.indiana.edu/novels/author.html

Project Runeberg
http://runeberg.org/wiki/Google_Book_Search

Link list on bible, judaism and christianity
https://umdrive.memphis.edu/mhooker/google_books-bible_judaism_christianity.html

Women writings in German
http://de.wikisource.org/wiki/Wikisource:Autorinnen

Bibliothek des Litterarischen Vereins in Stuttgart
http://de.wikipedia.org/wiki/Bibliothek_des_Litterarischen_Vereins_in_Stuttgart