The single most coveted tool is my pressure washer setup. I have put a lot of time, money and effort into this setup. Upgrading from an old Karcher, the flow rate and ease of connections transformed my washing process.
Now running Mosmatic gun and wand, MTM foam cannon.
Next, my detailing seat. It was a revelation when I discovered seated wheel cleaning, I went from hating wheel cleaning to loving it! Combined with my bucket setup, I look forward to taking and seat and just enjoying the process.
Sticking with the wheel step, this EZ-Detail GO brush has become a favorite tool for cleaning wheel arches.
On the subject of brushes, I absolutely love the new Detail Factory Tire Scrub Brush. These are slightly more pliable compared to the usual stiff bristle tire brushes, they seem to contour better. I love it so much I bought another for cleaning rubber floor mats.
My Blow Dryer, a big step up for me at the time and a crucial step when dealing with intricate front bumpers and grills. I'm trying out an EGO LB765 at the moment, but I think the dedicated blower is more efficient.
Sticking with air, my air compressor setup has become more and more useful. I added an upgraded hose reel recently, combined with new fittings. Also love the Tornador Basic blow out gun, especially on filthy carpet mats.
And lastly, my sink. This was another pivotal change in my detailing process, allowing me to fill buckets and foam cannons with ease, a workbench for measuring dilutions and filling spray bottles, and an ergonomic place to clean up brushes and other equipment after the detail. Love it!