Critique CircleOne of the best critique/workshop sites I've yet encountered. Lots of members, fairly short waiting time for story submission, interesting point system to ensure fairness in critiquing, and some of the most ingenious formatting systems I've ever seen. The software actually lets you create WYSIWYG inline critiques on the fly as you read. Very clever!
The entire setup is designed to protect your first publishing rights.
There's also an active forum and I've found the people there to be dedicated and friendly. What's more, the site also boasts a host of writing help tools (character templates, outlining program, etc.) and a nice database of links and articles on writing, editing and selling your work.