Among the first books I acquired in my research was an old copy of A Harmony of the Synoptic Gospels for Historical and Critical Study by Burton and Goodspeed. Before that I had heard others speak of the 'Synoptic Problem' but it was meaningless to me and just sounded like quackery meant to discredit the Bible. I have to say this one volume's laying out the Synoptic Gospels (Matt,Mark,Luke) without any commentary in a side by side parallel format rocked my world. I spent dozens of hours with colored pencil's highlighting exact phrasing and words. I got a little sloppy at times and missed stuff the first time through but it was abundantly clear what I was seeing was a literary dependence of one Gospel to another not simply independent witnesses confirming the accuracy of the story as I had been told. Two people can say essentially the same this but they will not use the same sentences and word choice. Sometimes it is as simple as laying out things carefully for comparison to see the process of composition and editing, seeing what was there all along but since we were told they were separate works we never noticed the obvious intertextuality. Here is a pic of my marked up book:
Since then I have found other similar works that utilize different translations and add more parallels to non-Canonical gospels and even quotations from church fathers. Here are a couple good ones.