We were going to use a ta but everyone kept finding better deals online. I have everyones itins and I used to work for an airline so i know what could happen as far as cancellations and such w/ using expedia, etc. So I frequently check up on my guests itins and will definitely do so more right before our wedding. Also since I worked for an airline at a smaller airport I have lots of friends at each airline who will help us w/ bookings and not having fees, etc.
So far it has worked out very well. Most of our guests have used expedia and orbitz for flights. Although my suggestion is if you or your guests find good flights from one airline on expedia, orbitz, travelocity, etc have them check that airlines site to see if the flights are the same price if so book directly w/ the airline. It will be much much easier if flights are cancelled etc so you can work w/ the airline and not have to deal w/ expedia or whoever. there are also some airlines who don't have contracts w/ expedia and such.
You also have some time, if I were you I'd wait 2 more months to book, unless you book w/ someone who will give you price guarantee. your flight dates are just now avail and if you wait a couple months they'll drop a little as they airlines know people are waiting for their dates to come avail to book.
Check out Airfare ? Cheap Airfares ? Cheap Airfare Deals they will show the good prices and you never know you just might find what you're looking for!