I use clipart as a base
on free jobs quite a bit (yeah, thats what you get when your church finds out you know how to design).
I usually heavily edit them, downplay them, turn them into vector art, etc.
My method of finding clipart, Google: "_____ clipart" haha
Attached is an example, the horse and cowboy was pretty static clipart, but Illustrator's livetrace as a "hand drawn sketch" added a nice life to it, in my opinion anyways.
(This project was done for a projector to be shown in a theater).
After this, I told them it was my last freebie, and to call me when they were willing to pay.
Edit: Very American, no? hahaha