School Glue (Clear or White)
Borax solution (1/2 cup borax to 1 liter water, best mixed in an empty pop bottle)
Food coloring
popcycle sticks

Directions:

Pour aprox 1/4 to 1/2 cup glue into a disposable plastic cup.
Put in a few drops of food coloring.
Pour 1/4 to 1/2 cup water (plain old water) into the glue
Add only a very small amout at a time of the borax solution and stir, the solution will soon start to thicken and adhere to the stirring stick.

The original recipe for this that I found through Amy says equal amounts of glue to water make sure you do that step right and small amounts of the borax solution. I added just small amounts at a time of the borax as needed while stirring until it was the right consistency. you will want to stop while it is still sticky as you roll with your hands the slime forms nicely and what was once stuck on your skin works itself back into the main ball of slime you are now holding.

Store in an airtight container in the fridge to prolong its stability.

My first attempt I used the 1/2 glue and 1/2 borax solution and it thickened really stiff and was kind of a bouncy ball except broke really easily when bounced a few times. Here's what it looked like.

Video tutorial