Here is my list, depending on the mood:

Stoner Comedy Classics:

• Up in Smoke (Cheech & Chong)
• Half Baked
• How High
• Harold & Kumar

Stoner Classics:

• Dazed and Confused
• Fear and Loathing in Las Vegas
• The Big Lebowski
• Human Traffic
• (2001 - A Space Odyssey)

Absurd Comedies:

• Airplane
• Napoleon Dynamite
• Hod Rod
• Tenacious D in The Pick of Destiny
• Anything by Monty Python for example Life of Brian
• Barb and Star go to Vista Del Mar

Visually Trippy Movies:

• Beach Bum
• A Scanner Darly
• Waking Life
• Glossary of Broken Dreams

Trippy & Weird Movies:

• Sorry to Bother You
• Sans Soleil
• The Holy Mountain
• Bakara

Drug Movies (trippy but not recommended if you are looking for a good time):

• Enter the Void
• Requiem for a Dream
• Trainspotting
• Spun (this one at least is still a comedy)

Edit: Bonus mention Dark Side of The Rainbow, that is Pink Floyd's Dark Side of the Moon synced to The Wizard of Oz