I seem to remember a resource (hardbound) which lists series of books which librarians used to get at what comes next for various authors. Online ones exist too--
http://www.fictiondb.com/series/author-series~c.htm
There seem to be other online resources as well.
http://www.readersadvice.com/ http://www.bettendorflibrary.com/bpl-bin/series.pl
The Big Names section of the Readersadvice.com is really helpful to series what's next for various populare authors--
http://www.readersadvice.com/readadv/000999.html