User Fields pending Admin Approval?
I set up a workflow for doing this using field permissions, rules, and revisioning.  It works at the node level rather than the field level though, and it's rather complicated to set up.  In my searching there was no single module able to handle this.

Basically, I used rules to create a workflow in which users can only create and edit certain content types, all of which are subject to approval either upon creation or edit (using revisioning).