There is no shortage of weird shows, but from the top of my head I can think of a couple!
Kuuchuu Buranko is a great one, characters often use live action for the close-up faces, and one of the characters is straight up a real person along side other 2D characters and pretty much everything in that anime's visual is insane. I have no idea how something like that was made, but I'm glad someone did it.
Kaiba is pretty unique, the visuals and the world of the show is weird, but very memorable. It's just a bit funny how horny it can be with
that art style.
The whole Jewelpet franchise is a fever dream, but
Jewelpet Sunshine is easily the weirdest one out of all seasons, some times I have to check some scenes again to make sure my mind dindn't just make up some fake anime. Not sure how much I would recommend it, though. If you need something weird from that series that is also more enjoyable, J
ewelpet Happiness is a better choice.
Paniponi Dash! is a classic. You don't have to do much outside of watching any opening from that show to understand why I'm mentioning it.
I also have to give a special mention to anything Ikuhara worked on,
Shoujo Kakumei Utena,
Sailor Moon S/SuperS,
Sarazanmai,
Yuri Kuma Arashi... etc. All those shows are extremely memorable for their surreal visuals, but I am particularly a fan of his silly humor.