I think the best piece of equipment I use now it the laser. But when I Was a school the thing that I liked most was a little turbine that would turn round just from the force of light shining on it. It was pretty impressive.
Just for fun, van der graaf generators are always a good laugh.
For “serious” science, I think I agree with Rob, the laser is a pretty amazing piece of kit. In my field, we use it to cool atoms, to trap atoms, to change the states of atoms, to make egg carton-like grids to hold atoms. We can change the shape of the light beam so that it twists and then use that light to twist atoms. We can entangle the beams. We can stir a superfluid and make an everlasting whirlpool.
And that’s just my area. I’m sure if you ask any of us, we can each give you ten different uses for a laser, and we still wouldn’t have covered everything.
Mine is hands down the Paul trap. It’s a set of three electrodes that can be used to trap ions in a specific location. You can do all kinds of funky things with them and the principle is pretty central to my current experiments. This video demonstrates them beautifully.