While I have a lot of favorite sites on the Web, if I had to chose just one, it would probably be Barbelith. Barbelith is an online message board whose members hail from all over the world, though most are concentrated within the United Kingdom. It was founded and funded by Tom Coates.
The word "Barbelith" comes from the DC Comic The Invisibles, written by Grant Morrison. In the comic, Barbelith is a mysterious yet benevolent satellite that orbits Earth, guiding the story's myriad heroes on their world-saving mission. Barbelith the Board serves a similar purpose, it's a place where one can go to give and receive feedback on a variety of subjects with the purpose of (hopefully) improving one's self and one's surroundings.
Let it be known, however, that while its name and some of its terminology may derive from the comic book, Barbelith is not an Invisibles fan site. It has no affiliation with either Grant Morrison or DC Comics. In fact, there are several long-time posters who have never even read an issue of the Invisibles.
The Barbelith Community prides itself on the literacy and progressive politics of its members, many of whom are in the journalism and education professions. Chatspeak is frowned upon (except in jest) and trolling is met with swift vengeance. If you come to the board bearing opinions that can be construed as racist, sexist, classist, or homophobic, your views WILL be challenged, sometimes to devastating effect. Similarly, if you are inclined to make blanket statements without the facts to support them, you WILL be called out.
Barbelith's design is simple and elegant. There are no blinking ads, no distracting avatars, and no other flashy bells or whistles. I find the soft pastel color scheme visually soothing, and the sub-forums are clearly labeled so that even a newbie can easily find or create a thread of interest. Also, if you need help with anything in the board, there is a handy wiki.
A fun feature on Barbelith is the ability to change your user name or "ficsuit" (short for "fiction suit", another Morrison trope) once a month. That way you're not stuck with Sardo Numsby, the ID that you came up with at 2:00 in the morning when you were so stoned out of your gourd you thought that The Golden Child was TEH COOLEST MOVIE EVAR!!!!11!!! You don't have to change your user ID if you don't want to-I've had the same ficsuit for the past two years-but it's nice to have that option.
One problem I've had with Barbelith's functionality is the search option. There have been times when I've looked for a thread I knew existed but the keywords I typed brought up every thread on the topic except the one I was looking for. Occasionally, but not always, I can get around this difficulty by using Google.
I've learned a lot from Barbelith. It was on Barbelith that I first learned how to create a link. It was from Barbelith that I found out about Zogg and the Leekspin Girl. It was through Barbelith that I discovered Tove Jansson's wonderful Moominland series of children's books. If I had enough of an attention span to read one of the more "serious" forums (such as the Switchboard or Laboratory) I might actually learn something useful.