I can't seem to find how to set a mouse button click to a regular attack. How is that done?
If you have "elective mode" on, you can just drag (with the left mouse button) the skill from the bar and drop it somewhere meaningless (e.g. on the main game area). If you don't have a skill in the "Left click" or "Right click" slot, then the melee will appear there instead. There are no options that I know of to put the melee on a number.
To activate "elective mode", you have to go into Options, then go to Gameplay, and then select "Elective Mode."
So, there you have it! :)
Elective mode doesn't allow me to bind regular attack to the left mouse button, but there is a way. Reassign whatever your left mouse button attack is to to right mouse button and the left will default back to regular attack. You can then change your right mouse button attack to what you actually want it to be. :-)