Origami Diamond:

 

A perfectly square piece of paper is needed for this. To quickly make a perfect square out of a rectangular paper, click here.

 

Take a perfectly square piece of paper.

Make these folds in it shown by the black lines in the picture.

For each fold, press it in both directions (press it down and then unfold it and press it down towards the other way this time).

Where all the lines are, the paper should be easily bent to the front or the back.

Leave the paper unfolded and go on to the next step.

   
The previous folds are now shown in light blue.

Make new folds, bending and pressing in both directions as before, where you see the black lines in the picture.

As a guide for where to make the new folds, notice how they begin and end meeting the previous step's folds.

Leave the paper unfolded and go on to the next step.

   
The previous folds are now shown in light blue.

Make these new folds the same way as in the last step.

Leave the paper unfolded and go on to the next step.

   
The paper should now look like this.
   
Where the black lines are shown, start to fold them down and under a bit so that it looks like the next picture.
   
At this point, keep folding the creases mentioned in the previous step.

From under the paper, poke the center point upwards or it might fold wrong.

   
It should now look like this.

The 4 corners start to become legs. Press them towards each other until they meet.

   
You can hold or tape the diamond at the bottom.

This is the diamond in side view.

   
This is the diamond in top view.