The first thing to come to mind is a Lincoln pneumatic grease gun. I only use it for greasing the metal-on-metal hubs of my old wheel disk (dirt molester you pull with a tractor for the city boys). There are a dozen hubs and it takes three tubes of grease to get them all. I used to spend an hour and KILL my hands and forearms from squeezing the pistol-type grease gun. Now it sounds like a machine gun as it pumps grease in. It's the best $60 I've ever spent.
Otherwise things like impact wrenches (electric, battery, and pneumatic), biscuit cutter, palm sander, 3-pulley drill press (goes slow for metal drilling), Fein Multimaster, Milwaukee portable band saw, pneumatic blind rivet gun (a real $400+ industrial Marson gun I got at a pawn shop for $45 because they thought it was a "paint sprayer"), old Allis Chalmers WD45 tractor and implements, Stihl chainsaws, farm/railroad jacks, and a host of other tools that make my life MUCH easier/faster/better.
Oh, as I have some baseboard trim to install after a carpet install last week, I'd better mention the Dewalt 12" sliding compound miter saw. It makes trim work quick (kinda, I'm a novice) and easy.