There are about a bazillion ways to make a homemade ornament;one favorite is the popcorn glass ball.
Buy a box of plain, clear glass tree ornaments. You an often find them at the dollar store during the holiday season. Take off the metal top, and fill the ball 1/3 full of popcorn. To pop the corn put it in the microwave on medium-high heat. Watch it carefully so it doesn't burn. Replace the top, add a red or green ribbon, and the results are pretty!
Another Christmas ornament idea that also starts with glass balls is the painted ball. These mimic those ultra fancy blown and spun glass balls. Again start with a clear glass ball, and remove the top. Next using crafters paint choose a few coordinating colors and add a few drops of the first color into the ball. Then spin or twirl the ball until the paint inside is thrown onto the sides and creates swirled patters. Let each color dry before adding the next color.