It's easy to remember the formula for volume of a cylinder if you know the area of a circle..  A cylinder is basically a tube, which has two bases, which are circles and a height.

So the area of a circle is Pi(r^2)

Think of the cylinder as a bunch of CD's stacked up top of each other until you reach the total height of the cylinder.  So it's obvious to multiply the area of the circle by the height to get the volume of the cylinder.