Do you ever use acrylic paint and hate having to wash out each brush when you're all done? Or maybe you're using several colors and one of them dries. I hate it too. Acrylic paint on your brushes can go rock hard in about twenty minutes and will ruin your brush.

Short Term Storage: If you'll be working with several colors at a time, simply get a dish with water in it and lay your brush in it while you work with the other colors. Preventing your brush from drying out. Remember to lay your brush in it, not stand it up on the head of the brush. 

Long Term Storage: I've found that if you save your brushes in a zip lock bag and put them in the freezer you'll be able to use them next time you need them. Note: Label the baggies with the name of the color you used. Yes, they'll stay wet (with the paint) and won't freeze.  You'll be able to dive right in next time you need your acrylic paint.