Every genealogist, whether amateur or professional, runs into a brick wall in the quest for their ancestors' histories. I came across a great book for opening up your mind to ways of getting around that brick wall. Check out Marsha Rising's Family Tree Problem Solver [2].
Links:
[1] http://hcpl.net/users/angel-hill
[2] http://catalog.hcpl.net/ipac20/ipac.jsp?menu=search&aspect=subtab13&term=family%20tree%20problem%20solver&index=.GH#focus
[3] http://hcpl.net/category/tags/genealogy
[4] http://hcpl.net/taxonomy/term/34