Doug Nash's
Hell's Gate is one of
the very best books on the Eastern Front. His sequel,
Victory Was Beyond Their Grasp, is one the very best books on the Western Front in 1944-45 (and it's got the best single chapter on the state of the Wehrmacht in 1944 I've ever read). You won't find a copy of
Hell's Gate under $100 because it was a fairly limited print run.
Bill Russ' book is a
very,
very detailed study of the Polish campaign from the German Army viewpoint. It is for serious students of history and wargamers. Not an easy read but an absolute mine of information and indispensable if you're studying
Fall Weiss.
Bloody Streets is a huge book - and absolute must for anyone studying urban combat/the Battle of Berlin.
For Eastern Front books with the emphasis on the Russian side, it's worth having a look through here:
WWII and other Book Reviews
and his Eastern Front library here:
LibraryThing | Catalog your books online
And we've not even touched on the German-language side yet.