hmm scifi.. It's not sci fi really, but Enter the Void is a unique film. shot in 1st person it explores the psychedelic realm with many references to obscure drugs that a psycho-naught would love. Refrences to DMT, Datura, GHB, LSD, Shrooms, Astral Projection, Death, Sex If you want a more sci-fi like movie, I always find the futurama films to have a fun laugh.. episodes are better though If anime is okay.. I have a million Bender's Game was good Documentaries can be interesting ways to, you could find hundreds on netflix I feel like I'm missing really obvious ones though..
2001 (at least I think the final act, anyway) and A Scanner Darkly definitely. The Matrix is only trippy the first time you see it, imo.
Wow, havent seen Scanners since it first came out, must DL and watch I assume you are asking for not so well known trippy ones, most mentioned so far were big hits, I mean who hasnt seen Inception. Lifeforce is a trippy one, early 80s British/American film. Puppet/Modelling effects that still stand up today even if the CGI doesnt People mention Butterfly Effect, The Jacket with Adrien brody was another good one along the same lines. Splice is another one with him thats pretty creepy Fantastic Voyage is a well known one, but an old one, one I really dont understand why they havent made a remake as its an awesome movie The Land Unknown (1957) an often missed goodie from that era
Although not psychedelic/trippy I perceive the whole movie as kinda surrealistic. Once you are aware there are litle til no emotions expressed in it for instance (did not notice that the first time I watched it). But also the excellent camera work/special effects, very creative and mind boggling to look at and figure out how they did it exactly
Under the Skin, currently playing film starring Scarlett Johanson, is one of the craziest alien sci-fis I've ever seen. I would describe it as a perfect cross between Species and 2001 a Space Odyssey. Amazing visuals. Was a perfect 4/20 movie, too bad I wasn't celebrating yet =P
John Dies in The End isn't quite sci-fi(maybe more like drug-fi?) I'm recommend it. I could never explain the plot well enough, but i'd suggest you check it out!