Similar to my question about the NPC Traders in Pokemon X/Y, I'm hoping to trade with all the NPC Traders in Pokemon Omega Ruby.
So where are all the NPC traders in ORAS? What Pokemon do they want, and what do they offer in exchange?
Since it's probably gonna take a longer while to make a full list, I'm making this answer into a community wiki, so anyone can update it as they find more traders.
Serebii has a running list that looks complete as of now.