One of the best and most intelligent magazines in America--"bound in 1857; unbound since 1993"--has a large and varied website featuring prose and poetry from the print magazine, archives, "web-only features," and a readers' forum, "Post & Reposte," that features, among other things, a place for people to post their own creative writing.
From 1957 to 1973, the Evergreen Review was a vital counterculture literary journal. After twenty-five years of dormancy, ER re-launched on the Web. Well worth visiting.
This site hosts many forums for writers to post their work for response by a very supportive community. This is one of my favorite places to post my poetry.