I am looking for some advice on wikis.  We have a special ed teacher that wants to use a wiki to do a project with her students and has no experience with wikis.  I am looking for a wiki that has a minimal (preferably none) amount of advertising and a really simple, uncluttered interface.  I am also wondering if there are wikis that can be configured to allow a moderator to approve edits before they are actually visible.  The teacher is concerned that there may be some 'vandalism' to the page if edits are published automatically.