For anyone interested in following the course of events on the Eastern Front by using maps, there is an excellent site that contains hundreds of detailed military-topographic maps in Polish-German-English & Russian.
The maps are principally Eastern European and cover Poland, White Russia, Ukraine, the Baltic states and Russia and many of them (especially the German ones) were published during the war and contain place names that were in use then. There are maps of almost all the areas where Germany & The Soviet Union would fight major battle in the coming months and years. Many of the maps are extremely detailed and also extremely large, so be warned.
The maps range from 1:100,000-1:300,000-1:25,000-1:500,000-1:750,000 and other scales. I consider many of them to be quite exceptional since many of the place and town names used during the war have changed since then. Click on the website and the maps listings are on the left.
By the way, they're free.
WIG Map Archives