A list of every item and block in the game.
Note: Requires some technical knowledge to understand
To ensure the accuracy of the item list, I decompiled Minecraft (though I don't use/can't find a de-obfuscated version) and searched for a few test items to find the relevant classes (note to anoyone DIYing this: bvs.class contains block IDs, and bkk.class contains non-block item IDs). Interestingly, any items which are placeable as blocks have their IDs listed only in the list of block IDs. To get the final list, one has to reference back and forth between the classes. I did so using a node.js program, and grep for debugging.
For blocks, it's much simpler. All I had to do was extract all of the relevant strings. no cross-referencing or bug hunting necessary.
If you think an additional list should be added, such as for older versions or things like entities or particles, make a comment or pull request and I'll check it out. Hopefully these lists come in handy for some people!