Blue Oyster Cult's "Don't Fear the Reaper" always trips me out...the lyrics, the music, even the singer's voice, all come together to have this sorta trippy, dark feel to the song. I love it.
It's a toss-up between: "The End" by The Doors "Set the Controls for the Heart of the Sun" by Pink Floyd "DMT" by Shpongle
the doors- the end, when the music's over, light my fire. pink floyd- the entire dark side of the moon. shine on you crazy diamond. the who- the entire Tommy. led zeppelin's dazed and confused live. kyuss- space cadet
helter skelter by the beatles..... also, the end, when the music's over, and light my fire by the doors and definitely it's so nice to have your love by country joe and the fish
A Small Package of Value Will Come to You Shortly- Jefferson Airplane. That song is a trip. Also, anything on Frank Zappa and the Mothers' album, We're Only in it for the Money.
Or even Hendrix's 1983...(A Merman I Should Turn To Be) or anything by the 13th Floor Elevators... "If your limbs start dissolving in the water that you tread..."