January 2013 E-Zine (V12#1): Marketing Thursday, Jan 17 2013 

Seek book reviews. Many reviewers will want a free copy to keep or donate, while some will work from a loaned copy or alternate edition. One can easily hand out more review copies than you sell, but targeted reviews can be worth their weight in gold.

This section is drawn from

January 2004, V3#1: Marketing Monday, Jan 26 2009 

Further online PR possibilities include working with your ISP to search newsgroups/usenet through your email program.  Once you find lists about your subject matter and review them, post information about your book.