The largest battle in the war, in fact, was in the Eastern Front. The Battle of Kursk killed over a million men, was the largest tank battle of the ever, and had the bloodiest day of aerial dogfights in the skies.
Nazi forces gathered a massive attack along the very eastern edge of the Russian Soviet Federative Socialist Republic (present-day Russia) in the flat steppe region in July 1943. The Germans planned to smash the Soviet lines by creating a bulge to punch out of and then encircle the Soviet army to cause a massive surrender like they did during the early days of the Eastern Front. It was hoped that they could reverse the loss of momentum after the Battle of Stalingrad and restart the invasion of Russia. They failed and the Soviet Union kept offensive momentum until the end of the war.
The bulge strategy was reused on the Western Front by the Germans during the Battle of the Bulge. It caught the Western Allies off guard in part because the Allies could not imagine the plan working in a forested hilly region. The hard fighting Germans nearly crushed the Allies and could have extended the Western Front via stalemate. Some historians say the Allies causalities and the emotional drain of a major lost after the disastrous Operation Market Garden could have stalled the war effort for over a year or two (though this does not factor in the Soviet advancing from the east against Germany). The Western Allies lost about 90,000 men compared to the Soviet loss of 800,000 at Kursk.
The semi-official RT has an English language program on the battle called Kursk: the burning bulge (also shown below). The program combines history and geography of the battle to paint a good picture of the events. It is something that would have been on the History Channel if that still showed history shows.