Schmoop: This site is an excellent resource for those nights when your thirteen-year-old comes to you after dinner, just before bedtime, and says she needs help with her thesis statement about Shakespeare and Anne Hathaway. It's not going to do the work for her, but it WILL help you help her or help her help herself. Also a great resource for other subjects, test prep, and it's put together by smart people from well-respected higher institutes of learning and such.
Crayola Printables: For serious. This site will keep them busy for HOURS. They will have your house decorated for the holidays in no time and learn a few things in the process. There are decorations, games, puzzles, and best of all, it's all FREE. I love free. Free is my language. Oh, and they have more than just stuff for Thanksgiving. Hit them up for birthdays, other holidays, and the four seasons.
Glue Sticks: Buy them in bulk. You will never have enough. You will never be upset you have invested in a metric fuckton. Keep them somewhere accessible. You will need them.
If you can afford it, an iPad or iPhone/iPod touch. SO. MANY. EDUCATIONAL, yet entertaining apps exist. Our kids are entertained any time we give them the opportunity to use these tools. I'll save my favorites apps for another post.