Last year I had the pleasure of seeing Andy Losik give a presentation where he used Apple's Keynote not to make cool presentations but instead as a photo and video editor. I was inspired by this and started to think about other ways to use Keynote and then I saw this article that included a bit on using PowerPoint to make your own royalty free clipart.
I immediately realized I could do the same thing in Keynote, so I decided to give it a try. As it turns out it was really easy. You can create some great clipart by using the simple shapes in Keynote and you'll never have to worry about Copyright or even Creative Commons attribution.
Once your figure is done, just select all the objects and Group them. The copy your figure and paste it where you need it. Your figure will be a PNG image with a transparent background. If you need to save your figure as an image file after you copy just open Preview and create a new image. A new image will be created with your figure in it already. Then just save and use as needed. Pretty cool.
Below are the figures I created one afternoon. Feel free to use them with a CC-BY-NC license, or just use them as inspiration to create your own.