If you're at a loss about what type of entertainer to hire for your event, consider a stage hypnotist. This is a fun, creative way to get your guests actively engaged in their entertainment, and you can be sure that hiring a hypnotist is something few people will expect.
Most people don't realize that a hypnotist can't make an individual do things they're morally unwilling to do. If any of your guests become concerned about this issue, be sure to reassure them that this is in fact the case; if they're unconvinced, be sure that the performer is told not to ask them to volunteer for anything.