Build this fun desktop catapult with only scrap wood, a couple of dowels and some rubber bands. Follow along at the link and see how it was built.
The whole trebuchet stands about foot tall when unloaded and flings various things ten feet or more. Moreover, this is a nice introductory woodworking project that you can do with mostly basic tools. Make sure to check all of the images. A lot of the details are in the notes there.