Some groups associate themselves with cyberpunk literature/scifi and call themselves cyberpunks, or, are associated with cyberpunk and called cyberpunks. The main classifications of cyberpunks are:

Hackers

Persons who are skilled or talented with most aspects of computers, software, electronics, and technology, and can do things with them that seem "magical". For hackers, technology is not just a hobby but a way of life.

Crackers

Sometimes called as "dark-side hackers". People who use their computing skills when breaking security on computer systems, for illicit gain or simply for the pleasure of exercising their skills. These are the real-world analogues of the "console cowboys" of Cyberpunk fiction. There's also software crackers, who open programs without paying, make patches, and change serial numbers.

Phreaks

Telecom crackers. They do a similar thing with the telecom system, coming up with ways to circumvent phone companies' calling charges and doing clever things with the phone network. Telephones are a phreaks primary interest. Many expand their knowledge to satellite and wireless radio communications. Scanners and counter surveillance devices, cellular phones and pagers are commonly used to maintain contact with the Internet and comrades around the world.

Cypherpunks

Masters of cryptography. Individuals who believe that the government is out to invade the privacy of everybody on the planet. The cypherpunk's central goal is to out-smart the system, and a good way to do this is through cryptography and cryptosystems. They believe widespread use of extremely hard-to-break coding schemes will create "regions of privacy" that "The System" cannot invade.

Netrunners

People who live in the Net and master it. Surfing, chatting, ircing, pinging, tracing, ftp:ing, fingering...

Otakus

Alienated computer nerds, mainly in Japan, fixated on manga/anime art, Net, and computer games - an obsession that in one case led to a string of horrific murders.

Ravers

These are the folks who use synthesized and sampled music, computer-generated psychedelic ("cyberdelic") art, and designer drugs to create massive all-night dance parties and love-fests in empty warehouses.

Transhumans and Extropians

People who attempt to exploit technology to increase human potential and life expectancy.

Zippies

Zippies, or cyber-hippies.

But, as the definitions say, cyberpunk is (intrinsically) undefinable and anyone claiming to be a "cyberpunk" may be laughed off any cyberculture community. It's also often so, that people who "should" be cyberpunks according to some definitions, don't consider so, or haven't realized it.

Essays about Cyberpunks in General

Cyberpunks

Timothy Leary's essay about cyberpunks.

Analysis of Cyberpunk Subculture

Analysis of a subculture group called cyberpunks, by Robert Weir.

Nerds with an Attitude

Are cyberpunks creative visionaries or merely nerds with an attitude? By Candee Wilde and David Weldon.

A Postmodernist Interpretation of the Computer Underground

A sociological analysis of the computer underground. Takes a look at the members and actions of the computer underground. An essay by Gordon Meyer and Jim Thomas.