Social and know-how

"Asahi Optical Historical Club"

The International Club of Pentax Enthusiasts, Historians and Collectors
URL: http://www.aohc.it/index.htm

"Pentaxforums"

Friendly Pentax discussionforum, also with reviews of new and old gear.
URL: http://www.pentaxforums.com

"Photo.net"

The large community of photographers with forums, reviews and galleries.
URL: http://photo.net

"Lightstalkers"

Journalists, filmmakers, photographers and professional travelers in a network. Lightstalkers is operated by November Eleven, a nonprofit organization ...
URL: http://www.lightstalkers.org

"Photocritic"

This site is all about learning more about photography, from the incredibly insightful (rarely) to the dreadfully mundane (also, hopefully rarely) via ...
URL: http://photocritic.org/

"Flickr"

The social image storage service which is probably the largest(?) You can use it as just an imagestorage or socialize within groups, discussions, use ...
URL: http://www.flickr.com

"Ipernity"

A webservice similar to Flickr but for all type of files and with some changes.
URL: http://www.ipernity.com/

"@TwitTogs"

A twitterrobot managed by @Photocritic
URL: http://twitter.com/twittogs

"PhotoChallenge.org"

A couple of different challenges, for example 2009challenge which is one theme a day.
URL: http://www.photochallenge.org

"Lens day"

Weekly photochallenge based on a theme. New challenge posted every wednesday.
URL: http://lensday.com