IguanaTex is a PowerPoint plug-in which allows you to insert LaTeX equations into your PowerPoint presentation. It is distributed completely for free. If you know how to use LaTeX, it is very easy to use IguanaTex. Select New Latex Equation from the Insert menu, and you will get a dialog box where you can type your equation. Need to change something in the equation? Just double-click on the image, and the IguanaTex dialog will re-appear so you can edit the LaTeX code; or, select the image and choose Edit Latex Equation from the Insert menu.
You can also treat the equation as an ordinary PowerPoint image. For example, it can be animated, rotated, moved, and resized.