I don't have any big tips, but some little things you can do that will save you some money if you haven't thought of them already are:
Bring as much as you can with you, such as snacks, bottled water, glow sticks/necklaces, film/batteries, little souveniers from dollar tree, the
disney store, etc so you aren't tempted to buy as much (more expensive there). That stuff can take up alot of room in your luggage, but since you'll be using alot of it while you're there you won't be lugging it back home with you.
Also, if you haven't already considered it, you may want to tell the kids that the trip is their Christmas presents and only get them a few things they need for the trip (disposable cameras, autograph books, fanny packs, etc) for gifts and use money you usually spend on Christmas to help pay for the trip. Also ask relatives to give kids Disney dollars instead of toys.
Start a change jar and pay for everything you can with bills, that little stuff adds up.
If you are a
AAA member, military or government employee, or have an AP there are a few more discounts to be found sometimes on tickets and/or hotel rates. As someone else said, Skyauction has gotten some great reviews for their condos.
You could join a rewards site like mypoints and try to earn enough points for a gas or food gift certificate to use toward your trip. It's free to join and you get points for clicking links in their emails, shopping through their links, and other assorted offers. I usually end up with enough points for about 2 cards a year, but I don't sign up for the offers and I forget to shop through them half the time.