I can't pick just one, so I'm going to cop-out with a top 3.

1. Meddle- Pink Floyd (turn it on when you first start smoking and by the time Echoes comes on, you'll be ready for it!)

2. II- Led Zeppelin (no words necicary)

3. Anthem of the Sun- The Grateful Dead (first one with Robert Hunter, letting the Dead flex their musical muscles. Best heard through good headphones)