Christianity has long been DC's official backstop religion. Unlike Marvel which routinely visits its various pantheons, de-mystifying them to a large extent, DC has the Roman gods, sometimes the Greek ones, and not much else, aside from, say, Rama Kushna.

Roy Thomas's JSA stories were largely predicated on the conceit that Hitler possessed the Spear of Destiny which pierced Christ's side while he was on the cross. In Thomas's continuity, it created a shield around Europe during WWII that effectively prevented the heroes from simply going in and ending the conflict.

The stories of Robert Kanigher often had a Judeo-Christian overtone to them, with Batman and Ragman praying in an issue of Brave and Bold or the soldiers who crucified Christ lamenting their involvement. An issue of Wonder Woman had a scene of a Jewish man praying over the body of a deceased Wonder Woman impersonator. One of the Sgt. Rock team-ups strongly implied that not only was Adolf Hitler still alive in the mid-70's, he was so because he was actually Satan.

Joe Orlando and Joe Kubert adapted stories from the Bible for an oversized Treasury edition. DC Christmas issues often smacked of religious themes, such as the Legion story where they set out to find the star that led Joseph and Mary to Bethlehem. Denny O'Neil strapped a would-be martyr to the prop of an airplane in his GL/GA run, with some strong Christian sentiments in that story.

Alan Moore's Swamp Thing visited both Heaven and Hell and specified the God of the Spectre series as being the Judeo-Christian one. Rick Veich tried to further entrench this idea with his Christ as a White Magician tale which did not see publication. Moore's Phantom Stranger was a consciencious objector to the War in Heaven. Grant Morrison's Zauriel was an angel who, as Kip points out, fought alongside the JLA in a Second War in Heaven, God help us... :-)

Of course over at Marvel, Angels were a part of Wolfman and Colan's Tomb of Dracula series, as was the Power of Christ as shown in the Silver Surfer guest appearance.

And yes, Mark Waid did establish that Jack Kirby was literally Marvel's God, with the power to restore a deceased Ben Grimm to life in a particularly ill-conceived series of issues of the FF. (All the more so because Moore had already rung this bell in his run on Supreme and Morrison has already pulled the "omniscient narrator restores dead characters" trick in Animal Man. By the time Waid got there, this story was already twice chewed...)

For real, full-on, all-out Christianity however, nothing beats the Dennis the Menace religious comics or the Archie Spire series. Man, Betty would get so enthusiastic about witnessing and finding salvation in those stories...!