This year, we won't be buying one; we'll be following the instructions we just found at greenUpgrader, and making our own.
All you need is some scrap paper, a printer, some cardboard from the recycling bin, and a few tools. GreenUpgrader even gives you some downloadable PDF week and month pages.
Here are all the instructions. We think this is a pretty easy project for even the most novice of crafters.