Essential reference for MS/JH

[James Perkins <jperkins@PO-1.STAR.K12.IA.US>]

I would be interested to learn what LM_Netters would consider as essential
print reference tools for the middle/junior high school media center.
(Please skip the encyclopedias and dictionaries.)  We have some $money$ to
spend, and would like to hear about some of your favorite titles.