I find lists of book series very helpful to me so know what to look for and I can mark them off as we go, and having that list in chronological order is what I look for. So I thought I would pass these two series lists along in case it may be of use:
Childhood of Famous Americans in order:http://www.redshift.com/~bonajo/COFA.htm
Landmark World and Landmark American History:http://www.pattysbookshop.com/home/landmarkserieschronologicallist.html
BTW, Paula's site, Valerie's Living Books site and the 100 and 1000 Books to read sites have awesome lists, even listing out living math and science books.