You will need:
Colored Construction Paper
Staples (works best) or Glue
Cut 1 inch strips of paper. Make each strip into a loop (overlap ends and staple or glue together) and link them all together to form a long chain. Make enough loops so your child can take one off every day from now until the date your counting down too!
Hang it high on the wall so they can reach the bottom loop! I also write numbers on mine so its easy to make sure there are the correct number left. Sometimes my daughter takes two off in one day, or forgets to take on off. It's a great decoration too.
I have used Paper Chains to countdown to lots of different events. If your child is learning their colors it can also be a great way to practise those. When they take one off they tell you what color it is (use lots of different color paper).
I always make countdowns when Daddy's deployed. Usually when there are around 30 days left until he comes home. Got a little carried away once and made over 100 loops. I hung them from the ceiling like garland all around the room. My daughter was learning her colors then....