At long last, a post approval plugin for Vanilla 2!
PostApproval was custom-developed to provide moderated post pre-approval functionality to a specific forum, and since then I have decided to tidy it up a bit and release it publicly. It's not perfect yet, and lacks in config options, but overall seems to perform rather well.
The basic function is simple: All new discussions and comments are invisible until approved by a moderator. A user can see his own hidden posts and discussions, so no risk of double posting. Posts retain their original post date when approved, so comment structures in discussions remain intact.
Moderators can see all pending posts when viewing a discussion as normal, and each pending post is clearly labeled so none will be missed. Moderators can also opt-in to receive email notifications when a new discussion or comment is posted that requires approval, and with a single click from within the email can instantly approve the post.