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Do a search on Yahoo or Alta Vista or your search engine of choice on
the phrase "clip art" and you'll get lots of sites. Some of them are,
granted, too cartoony for your purposes; others are much too
special-purpose. However, I've found some good sites with usable clipart
when I needed it.
Be aware, however, that one of the urban myths floating around is that
clipart is THE most common way to import a virus. Play safely.