This is a classic. Apparently the author, Tom Wolfe, never actually took LSD, but he still does a great job conveying the mentality of the era through what is often called stream of consciousness writing (there's a journalistic term for this as well, but i can't remember what it is).
The book chronicles Ken Kesey's first drug experiences and continues through the beginning of the Merry Pranksters and the Acid Tests. It sums up the attitude of the era through the style of speech, and it also reminds the reader that all the characters who we know of as hippies, acid testers, etc. were also real, 3 dimensional people with personalities and feelings. It almost makes me feel like i'm there with the pranksters whenever i pick up this book.