Of the tools I use more frequently, currently my favorites are a Japanese calligraphy nib holder made of wood with a silicone grip, a set of diamond bits to drill glass, and a 20mm bamboo crochet hook.
With that said, I am a fan of super-specific tools, those you buy knowing that they will only serve a single function. You may not use them that often, but when you do need them... such joy!
My two favorites are a steel erasing shield, and a jig/vise miter cutter.