We have a Forum-style section at the bottom of the page (on our DEV sites) where people can add a Comment. The ideas is that a Tester, finding an issue, will check the Comments at the bottom of the page before adding a new (possibly duplicate) Comment.
We allow Assignment of the issues, internally, and then Assigning it back to the Author for Approval, once it is fixed.
Additionally testers mark the page as "Operational" or "Broken". We have a report of pages not-yet--reviewed - so testers can make sure they have achieved 100% coverage.
We have routines that will reset all pages to "Test required" (ready for another round of testing), optionally leaving pages marked as "Broken" at that status, or resetting everything to "Testing required".
We tend to use sub domains for this - so TEST.MyDomain.COM - and have the ROBOTS.TXT set to disallow all search engine spidering - so only those in the-know will find the site. (I suppose you could be more paranoid, and require password-access, but our clients are about to launch the site and not paranoid about outsiders seeing it - indeed, they often ask Customers etc. to have-a-look)
Having said that we do have a "Known user login" which proffers no specific admin powers, but does log any Comments to that specific user - always useful if we can't work out what the heck their Comment actually meant!