Balloons
Buy solid color balloons and then download the pdf here for the face templates:
Angry Birds Balloon Templates from the Party Blog.
All you need are balloons, scissors, and tape.
NOTE: If you plan to tape, hang or attach the balloons to a wall or window, you can use the small helium filled balloons. We found that after taping the pieces on the balloon, it was too heavy and did not float unassisted. We also found that if you tried to move or adjust the piece you taped on, there was a good chance the balloon would pop. We recommend you decorate the balloons right before the event as a precaution and have a few extra. If you want a group of floating balloon as in our photo, use large mylar balloons.