Sheets, Bedding, Towels - it's a well-known fact that January is the time of White Sales... so that means Towels and Sheets at 50% or better.
Video Games - all the new stuff came out in time for the Christmas rush, so if you procrastinate (or just delay pleasure) you should be able to find some good deals starting right about now.
Winter Clothing & Coats - whether it's just the winter/fall collection or an actual coat, now is the time to buy it. There are always some good styles that never go out of style so you don't have to worry about them not being "in" when the weather cyles back around to be cold... then again, in most of the country you've still got at least a couple more months of cold weather to enjoy that new outfit or coat.
Boats/ Campers - not too many people get out and go camping or enjoy a day on the lake when it's 20 degrees outside, so you can guarantee you will find some good deals on the outdoor toys right about now (unless you are wanting a snow-mobile, in which case you may want to wait till July).
Christmas Decorations and Wrapping - if you can find any left, now is the time to buy them. Most stores start marking these items down the day after Christmas (at the latest), and many are cutting the prices as early as the first of December just to avoid having to deal with it after the holidays and to make sure they can get Easter out as early as possible.
Furniture - new models of furniture typically come out in February, so start hitting the stores in January when they are trying to clear space for the new stuff, and get last year's models cheap.