I compiled a pretty good clip-arts that I found from a free stock photo website called "Kozzi Images." I've seen lots of good stuff there. Here's a sample Clip-arts:
Mythological Characters Clip-arts:
Cute Business Machine Clip Arts:
Actually, I tried to make Clip-arts of my own using Photoshop but every time I make one, the result is always not good. Seems like I have a long way to go to make as beautiful as these clip-arts above. "Patience is Virtue."