Check out this nifty little marble machine kit from the folks at RetroTime. The most unique feature of this little marble track is the arm that lifts the ball bearings to the top of the run. A geared hand-crank powers a small arm, something like one you might see on a catapult. No, it doesn't throw the ball bearing. (Sorry, if I gave you the wrong idea.) It simply places the steel ball at the top of the track with a smooth motion. It looks as if you can effortlessly keep marbles flowing down the track at more that one per second. It creates a nice rhythmic motion and sound that I find soothing.
The kit includes laser cut wood components, steel balls, a screw pack, sandpaper and wood glue. The product page for the kit also features a nice tutorial video.
Here is where you can get this laser-cut marble machine kit.