What's the exhaustive set of items I can use to make Dwarven Metal Ingots?

From UESP, here are all the items that can be smelted down and their ingot/weight

• Small Dwemer Plate Metal (1.5)
• Large Decorative Dwemer Strut (0.1333...)
• Bent Dwemer Scrap Metal (1.5)
• Large Dwemer Plate Metal (1.5)
• Solid Dwemer Metal (.2)
• Large Dwemer Strut (.15)

Of the three items that melt down to a ratio of 1.5 ingots/weight, they all weight 2 and produce 3 ingots from the smelting and thus are the most valuable to collect.

Of note from the uesp entry:

You are liable to find many other items in dwemer ruins that look metallic but can't be smelted. An easy rule of thumb is that if it starts with the word "Dwemer" (dinnerware, cogs, gyros, etc.), it can't be converted, not even Dwemer Scrap Metal . Bent Dwemer Scrap Metal can be smelted. The Small Dwemer Lever is an exception; its name doesn't start with Dwemer, but it still can't be smelted.

As usual the UESPWiki has the most coherent collection of information on this topic.

The basic idea is that the two different plates and the scrap metal are "worthy" of collecting:

• Small Dwemer Plate Metal
• Large Dwemer Plate Metal
• Bent Dwemer Scrap Metal

Each of those will produce 1.5 times their weight in Dwarfen Metal Ingots (don't ask me how the physics of this works out). Interesting sidenote: the Large Dwemer Plate Metal and the Small Dwemer Plate Metal are effectively equivalent on every stat, despite their names suggesting differently.

The other stuff is not usually worth it, unless you don't worry about carry weight. The problem with those, is that they produce a lot less Dwarfen Metal Ingots than their weight would suggest (in decreasing order of ingots per weight-unit produced):

• Solid Dwemer Metal
• Large Dwemer Strut
• Large Decorative Dwemer Strut

Any other "Dwemer" item that is on neither of those two lists can't be smelted to produce Dwarfen Metal Ingots at all: it's vendor thrash (or used in the occasional quest).