Here's an easy way to recycle paper and organize your index cards at the same time. This origami box is a modification of the one on this site: http://www.origami-fun.com/origami-rectangle-box....
-regular printer paper
-pen or pencil
Step 1: Fold and Unfold Hot-dog Style
Fold and unfold the paper along the long side.
Step 2: Fold Both Sides Towards the Centerline
Step 3: Fold the Edge at the Center Line on the Back
Fold the two flaps outward and in half and make sure the edges align.Turn the paper over
Step 4: Fold Edges Toward Center
Step 5: Fold Left Corner
Make sure bottom edge of corner touches the rightmost crease.
Step 6: Fold Corner Under
On the top band of the folded corner, fold the corner under the band.
Step 9: Draw Line
Line up an index card with the top of the paper. Draw a line at the bottom of the card.
Step 10: Fold Bottom Up to Line
Make sure the bottom of the band lines up with the line you drew in step 9.
Step 11: Fold Back
Fold the right side of the corner back so that the edge lines up with the right crease. Also, fold up the bottom.
Step 12: Unfold
Mark the crease created in step 11
Step 13: Cut Along the Crease From Step 12.
Step 14: Repeat Steps 5-7
5. Fold corner to crease on right
6.Tuck corner of top band under.
7. Fold the right corner up and under
Step 15: Tuck Point Under
Step 16: Form Box
Crease the base of the box and pull edges upward until it forms a box.