I used to have a wonderful kaleidoscope as a child. A big heavy duty one. I can't find a good one but today I bought a cheap one from the works and its actually quite good!
Other visual stims I like are watching hand movement ASMR videos, especially ones where they spin their fingers, and ones where they use light 'triggers'. I'm also partial to a good snow globe.
As a child, my favourite was to push on my eyelids as it would create lots of swirly, colourful patterns.
Anyone else have/had a visual stim?