If you have a table saw, radial arm saw, or miter saw, you can get a triple-chip blade for it.
The triple chip makes nice smooth cuts in plexiglass as long as it is sharp and you run it slowly through the blade.
regular table saw blades will tear out the bottom of the edge and make it pretty ugly.
Another neat trick with clear plexi is that you can run a propane torch lightly on the cut edge to turn it from milky white to clear.
It also evens out some of the machining marks from the saw.