I'm a fan.
Fear & Loathing is the best place to start. By the end you'll know if you really need to read any more of his stuff as you'll have a complete grasp of his social and political outlook which dominates just about everything he writes. He wrote a column for espn.com for a while, just search "hey rube" from their main page. If you are digging that, then I would definitely recommend Fear and Loathing: On the Campaign Trail '72, & Hells Angels, as well as The Great Shark Hunt.