I have two votes:
1.) CC and BCC for sure. We primarily deal with email tickets, and our clients always copy other people on the emails. This should be standard practice if you are dealing with email tickets to make sure all parties are notified of ticket updates.
2.) Waiting for Reply Status (Similar to 1.6 Mods "Pending Status" and "Simple Status" - Coming from someone who manages hundreds of open tickets, not having a different Open Status is a problem. A proven suggestion is this:
When updating a ticket, at the bottom next to the update/send button, have 3 different statuses (Open, Waiting for Reply, and Close), with the default being "Waiting for Reply".
When you update/reply to a ticket as "Waiting for Reply", it puts the ticket into a separate queue on the same page as the users open tickets. Effectively, the user will have two groups of tickets in the Open tickets Tab, 25 "To be Answered"" tickets and 25 "Waiting for Reply" tickets.
Consider also having the option of setting a default status for Staff created tickets.
I currently use this method with Cerberus help desk, and I would never go back to a different way. Don't get me wrong, Cerberus is a fantastic Help desk, however, my staff sometimes have a hard time getting used to the complexity of the feature set, and I'm looking for a more simple solution.