If you see a bonus (particularly on legendaries) that is out of the range I've given, let me know. I suspect some of these items have a smaller range listed in the Blizz database because they are low level legendaries, and the +%dmg range may actually increase when those items are rolled with lvl 60 stats. If people have some of these legendaries, they can check the ranges by holding down Ctrl. I have very few of them, so I could not check these things. Also, this list does not include pre-2.0 items (hopefully).
My goal here was to say i.e. "I want to run a Frozen Orb build, what is the best % dmg boost I can get in each slot?". 15 to orb in helm, 15 to cold in amulet, nothing in shoulders but maybe I could run Blizzard, 15 cold from Frostburns on hands, 15 to Blizzard on chest, 15 cold on bracers, 20 cold on SOJ, nothing on belt/pants, 15 to orb on boots, 20 to cold on Lidless Wall or 15 to orb on source, 20 to cold on Azurewrath. All told, +85% cold, +45% to orb, +30% to Blizzard.
Pietrak was also kind enough to remake this as a google spreadsheet , for those that wish to view it that way. It has filters, which you can use if you make a copy of it. I am keeping the google doc updated as I make updates to this page.