I'm no historian, but I do know of one failed bombing called the July Plot.
Leaders of Germany's failing military headed the plan, codenamed Valkyrie. On July 20, a briefcase with a bomb in it was left in a place Hitler was known to be. "Bad luck and indecisiveness thwarted the plans. An attending officer had nudged the briefcase containing the bomb out of his way to the far side of the massive oak support of the conference table, which thus shielded Hitler from the full force of the explosion. A stenographer and three officers died, but Hitler escaped with only minor injury."^(1) 180-200 plotters were discovered and disposed of.
One of these likely plotters was Dietrich Bonhoeffer, well known in Christian circles as a pacifist minister who stood against the Nazi party. This was stark contrast to many other German churches, who were influenced by Nazi ideology (e.g., Bonhoeffer believed that Christian Jews had the same rights as non-Jewish Christians).^(2) He wrote several works, one of his better known being The Cost of Discipleship (1939), the title of which demonstrates the stress of standing for values different than the government. His involvement in the plot seems to go against his pacifism; it demonstrates their desperation in believing that the only way to handle the problem was through a coup d'état. He was arrested due to his opposition to the party in 1943. After the July Plot, documents connecting him to the plot led to his execution on April 9, 1945, less than a month before the end of WWII.
In addition to the groups already named, there was a Jewish resistance/terrorist organization known as the "Baum Group" active in the late 30s and early 40s. It was lead by Herbert Baum, and mostly engaged in pamphleteering and other such forms of clandestine but non-violent resistance, with the aid of its non-Jewish members.
In 1942, the group attempted an arsonist attack against the "Soviet Paradise" exhibit put on by the Nazi government, an exhibit which was supposed to showcase the horrors of Soviet Russia under "Jewish Bolshevik" rule. The attack was unsuccessful, though the exhibit was partially damaged.
The "Baum Group" was shortly thereafter broken up by the Nazi authorities, and its members arrested and executed.
My main source is Saul Friedlander's The Years of Extermination.
Some more here.