I always love to draw my own pictures. Once an aspiring art teacher, I decided to go for elementary education instead because my art high school teacher told me I wasn't good enough. When I taught math, I kept my students' interest by drawing as I taught. I drew characters like Greatest Common Factor Man and Tater Tot Girl. The kids even got into the act and made posters of the characters for our room.
I found a great post on Educational Origami that lists a lot of great sites for drawing your own cartoons if you want to add a little spice to your teaching. Kids do love this kind of thing. I'm sure they'll turn out better than some of mine! Trust me, the list is just awesome and well worth a look.