Website / ConceptArt.org
is a nonprofit company founded by Jason Manley, Andrew Jones and Coro Kaufman. It includes a forum, targeted towards professional artists working for the entertainment industry, but is generally welcoming towards neophytes too.
Occasionally, artists will come in from DeviantArt
expecting to be bitch-slapped into submission. Apparently, that's the sort of reputation the site has over there. They do have a Critique Forum, new users are usually given a fair critique by whoever has spare time, which is sometimes nobody, a fact that the mods keep working to change.
This website provides examples of: