Of course there’s a lot more to be found, but I stumbled across these and the first one listed got me to spend time on the rest.

The rules are simple:  Stare and the screen, then look at your hand. I saw this a few years back and had forgotten how well it works.

See over 100 posters by the late Rick Griffin. His work included a lot of album covers, probably most recognizable in his Grateful Dead covers, as well as Zap Comix.

Visual Overdose, Energisers and other Crazy Images from Eyvind Almquist of Virtual-Exp Psy.

Java-Fuxation and many other trippy voyages from Entropy8zuper, the people who brought us Venus Trap

There’s a lot more LSD inspired/related links at Best Psychedelics in the World, which is where these came from. Some have cool graphics, some are historical, some are just pro-acid articles. Go for the graphics.