Tonedeaf,
I'm not sure the IS one forum. There are lots of 'em...but catering to specific groups of people.
http://nikonians.org/forums is a pretty good site that discusses all things Nikon. (Being a Canon user, it's probably best described as a site where the endless pursuit of the lastest gear transcends all notion of the "photograph" being at the center of attention!) But it does have discussions on Panoramas, Underwater photography, Technique, Post-Processing and much, much more.
http://photo.net has Canon forums
Here are some sites that, in turn, will give you lists of other photo sites.
http://www.afterimagegallery.com/sites.htmhttp://www.digitaljournalist.org/http://dvnetwork.net/ (at left of home page there are dozens of great links)
http://www.photoeye.com/If you are trying to understand post-processing, and
specifically, working with Adobe's Photoshop Lightroom, I have a whole list of sites that are very good at explaining details, complete with video clips, presets you can download free etc.
Hope that helps.