Today is ONE of the best days to buy for next Christmas. As awesome as it sounds, the "Clearance" items you see on sale today will most likely still be there for a week or so and their prices will continue to plunge.
So, my advice to you is this... If the items you want to buy are in large quantity, then you can probably afford to wait a few days to buy them. But, if you have your eye on a one of a kind Christmas ornament, or decor in general, buy it as soon as it goes on sale!
Year after year I find myself missing great deals when I don't buy the Christmas decor I see when I first see it. This is especially true at shops like Hobby Lobby and Michael's. Granted, both stores will take their products down to 80% off, but the selection at that discounted price is not usually very good.
I also highly recommend that you search your local Craigslist or Classifieds for items you still want to buy. For example, every year there are hot new items on the market; this year the iPad 2 and large flat screen tv's are especially popular. If you are in the market for a tablet or tv, but aren't concerned with purchasing the top of the line models, then you'll be able to find a host of older models on sale in January. Once people get into their new item, the "older" model starts collecting dust and they realize they would rather have the cash, so it's a great time to purchase gently used electronics (gaming consoles, games, computers, tv's, cell phones, etc.).
January is also a great time to buy winter coats and clothing for next year. I usually purchase clothing 1.5-2 sizes larger than what my children are currently wearing. I've found so many great deals using this method. I purchase, pack away and then, when it's time for the new season, we get to open up and wear brand new items we had forgotten that we'd purchased! It's like a gift from yourself! I always shop at Gymboree, Crazy 8's, and The Children's Place for their clearance items. They have great sales, and Gymboree's Gymbucks are activated mid-January.
If you have money-saving methods for post-Christmas sales or planning ahead for next year's Christmas season, tell me what they are and what's the biggest benefit to them. :)