You can't go wrong listening to Terrence McKenna, unless you go away believing everything he's said to you. My first encounter with him came via Bill Hicks who briefly cites him and the so called "heroic dose" in one of his stand up routines. This meant that the name was stored away in a file marked 'some sort of intellectual clever man'. Actually, Terrence, is more interesting than that.
Firstly, the more controversial point of view which he held was that psychedelic drugs are good for you. It's a shame that this idea instantly puts off a good 80-90% of people from the get go as they'd benefit from his other ideas. McKenna is a raconteur in the truest sense. He jumps from idea to idea like a frog with a cheeky grin. He's the authentic voice of ideas which you don't encounter in 60's/70's nostalgic TV retrospectives but which formed a huge part of the dialogue of those decades.
Here's a few good YouTube vids to get you started...
NOBODY IS SMARTER THAN YOU ARE
CULTURE IS YOUR OPERATING SYSTEM