#1 - A big high-quality tool chest
I don't use my tools for work (anymore), so I can't justify the expense of dropping a couple thousand dollars on a tool chest. All it does is give my tools somewhere to lie down at night right?
Instead I distribute my tools between a 46" Husky mobile workbench, a 27" Husky top box I mounted to a cart and a 27" Waterloo tool chest combo - and then my shelves and work benches. My tools don't all fit, which means I have made a hobby of perpetually re-organizing things. I just feel life would be simpler if I had more space - but when deciding between money for a box and money for new tools, I always seem to choose the latter.
#2 - A metal lathe
Even just a mini? I just think it would be neat! But then I know I'd want a mill...
#3 - A welding torch
I've got a little mig that gets me by, but I could do more dammit!
#4 - Bigger versions of all my shop tools?
I feel like I have the basics covered, a drill press, bench grinder, wood lathe, bandsaw, polisher, etc... but wouldn't it be nice to have more capable versions of all of them?