Part of this may fall more under tool accessory than tool, but my first revelation came after setting up a VFD.
I always thought "surely a 3 or 4 step pulley is enough", and while it's certainly better than nothing, it doesn't even touch the versatility and convenience of a VFD.
2nd: A horizontally capable grinder. Whether it's a stand alone, or a tilting machine, I never realized how much I needed one or would be using one.
Lastly, and kind of encompassing all of the above: A quality 2x72.
I started off with a NWGS, which is a fantastic and very capable design, but it was still lacking, overall. Ultimately, I ended up designing my own, as no single machine had everything that I felt I wanted or needed: Quick and easy belt changes, tool-less adjustments, tilting, direct drive, multiple tool slots, VFD, etc...
My work flow and efficiency has vastly improved, and I'm able to do more than I ever could on a basic machine. One day I'd love to have 1, 2 or even 3 more just like it.
