Robert Stone is the absolute best. First of all, his writing is American Realism at its finest. And second, he provides counter view on the counter cultures of the 60s and 70s. While other writers really focus on the "groovy! we changed the world" stuff, he mercilessly chronicles the dark sides. Strongly recommend "Dog Soldiers" as a good novel to start with, as well as his his memoir, "Prime Green."
Dog Soliders was also a big influence on William Gibson[1], I see a lot of stylistic similarities.