Have there come to light any plans either by the allied forces or those within the Third Reich to depose/disgrace/assassinate Hitler himself, rather than just plans to crush his forces?
There were a number of attempts on made on Hitler's life, some notable ones were
One of the earliest attempts was made by Johann Georg Elser on November 8, 1939, when he placed a time bomb, at one one of the columns behind the podium, where Hitler gave a speech at the Burgerbrau Beer Cellar in Munich. The Bomb missed its deadline by 8 minutes, and Hitler lived to die another day.
In 1939, prior to the outbreak of WWII, Wermacht General Kurt von Hammerstein repeatedly attempted to lure Hitler into visiting the Army’s fortifications along the Seigfried Line near the Dutch border where he commanded a base. Hammerstein and his co-conspirator, retired General Ludwig Beck, had planned a ‘fatal accident’ to Hitler during his inspection of the base. Hitler however, never honoured the invitation, instead he turned the tables on Hammerstein by placing him on the retired list.
Another plot to assassinate Hitler was hatched at Army Group B Headquarters near Ukraine by General Hubert Lanz, his Chief of Staff, Major-General Dr. Hans Speidel and Colonel Count von Strachwitz. Lanz stated that he would have then arrested Hitler, and in the event of resistance, Strachwitz tanks would have shot and killed the entire delegation. Hitler cancelled the visit and the plan was dropped.
At Smolensk, on March 13, 1943, Colonel Henning von Tresckow together with other officers, plotted to blow the plane on which Hitler, was flying back to Berlin, by concealing a bomb, in a brandy bottle, presented to Colonel Heinz Brandt who was flying back with Hitler. However the bomb failed to explode, owing to the high altitude of the flight.
On March 20, 1943, Colonel Rudolf von Gertsdorff, General Kluge's chief of intelligence, tried to kill Hitler in the Zeughaus. The concealed bomb was to be detonated by acid while he stood close to Hitler in the exhibit hall. Unfortunately Hitler left the building before the acid could act and Gertsdorff immediately entered the men's room and flushed the fuse down the toilet.
On March 11, 1944, Cavalry Captain Eberhard von Breitenbuch decided to assassinate the Führer by shooting him in the head using a 7.65mm Browning pistol concealed in his trouser pocket, but was not able to carry out the plan because SS guards had been ordered, earlier that day, not to permit adjutants of officers into the conference room with Hitler.
In February, 1944, Infantry Captain Axel von dem Bussche agrees to blow up Hitler and himself while he demonstrates a new army winter overcoat to the German leader. Fate intervenes the day before when during a British air raid the uniforms were destroyed and Bussche was returned to duty at the front. A few weeks later another ‘overcoat’ attempt was made. This time the volunteer model was Ewald Heinrich von Kleist, son of one of the original conspirators and included Major General Helmuth Stieff. Again the RAF saved the day with an air-raid just before the demonstration was about to take place forcing its cancellation.
Lastly there is the famous attempt by Lt. Colonel Count Claus Schenk von Stauffenberg, on On 20 July 1944, near Rastenburg, East Prussia. He Concealed a time bomb inside his briefcase, which went off as intended, but did not have the right amount of explosive or was not positioned in the right place to inflict any serious damage on Hitler. Read more about the plot here.
After surviving many attempts on his life, Hitler intensified the Propaganda that he was chosen by the Providence/Creator, to carry on his mission in Germany. I quote Hitler after one of the assassination attempts:
Few people can begin to imagine the fate which would have overtaken Germany had the assassination attempt succeeded. I myself thank Providence and my Creator not for preserving me - my life consists only of worry and work for my people - I thank him only for allowing me to continue to bear this burden of worry, and to carry on my work to the best of my ability.
Adolf Hitler speech after surviving assassination attempt, 20 July 1944:
Once again I take this opportunity, my old comrades in arms, to greet you, joyful that I have once again been spared a fate which, while it held no terror for me personally, would have had terrible consequences for the German people. I interpret this as a sign from Providence that I must continue my work, and therefore I shall continue it.
There is a good documentary made by the history channel on the subject of assassination attempts on Hitler, here is a YouTube video , of the said documentary.
The most serious attempts came from the Wehrmacht, probably the only organization that had a chance. As reported in sources such as William L. Shirer's "The Rise and Fall of the Third Reich," in 1943, General Henning von Treskow planted a time bomb in Hitler's private plane that failed to go off.
A more serious attempt was made by Count Colonel Klaus von Stauffenburg on July 20, 1944, after the Normandy landings. It also involved a time bomb, planted personally by Stauffenberg, who "abandoned" his bomb-loaded briefcase while he was sitting next to Hitler. Unfortunately, another general moved the briefcase, thereby sparing the dictator.
That's because Stauffenberg had left the room with plan to lead a coup d'etat against the Nazi party once the news spread of Hitler's death. As it were, no such news came, the conspirators hesitated, and were soon rounded up and executed by Nazis acting under Hitler's orders.