depends what kind of stuff you are looking for:
German:
The Soldat Series by Cyrus Lee are WONDERFULL. they each cover a specific period in the war and go over the uniforms and acounts from that period. go to
http://www.soldat.com/soldat_books.html
US:
Just about anything that isn't from Time-Life check out barnes and noble. (I don't have many books about the US military except for the Army Air Forces, my first love)
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"Victory at any Price!"
SS-Panzergrenadier