This site could just as well be called "Beatnik 101". It's a real good introduction to beatniks of both stripes, the real "Beats" and the stereotyped weekend wannabes. Here's an excerpt for your perusal:
"The Beatniks we know and love, with their requisite bongos, berets and turtlenecks, made their big screen debuts in Hollywood films like FUNNY FACE and BELL BOOK AND CANDLE in the late 1950s. They weren't called beatniks yet, but they were black-clad, modern-dancing, angst-ridden Existentialists—a trés chic French export. These early beatnik stereotypes—goateed, bongo-beating espresso drinkers—were then portrayed as quaint and harmless, if somewhat silly.
But in American urban centers like New York and San Francisco, a youth culture that defined themselves as "beat" was forming. These were members of a generation whose spirits were beaten down by World War II and the new fear of atomic weaponry, and responded to the angst by rejecting the materialistic, straight-laced values of the 1950s mainstream. They listened to jazz. They experimented with drugs. They wrote stream-of-consciousness poetry. They danced to the beat of a different bongo, and went pretty much unnoticed. It was only after the publication of Jack Kerouac's On the Road in 1957 that the mainstream caught on."