http://slodive.com/design/best-sites-for-getting-free-vector-art-images/
A couple of the sites have limits on how many times you can print each image (negating this if you incorporate the image into a different image of your creation) and in some cases ask that you credit the copyright holder or link back to the site when possible.
That said there is an awful lot of free art there.
That's pretty cool. I don't personally use vector art regularly, but that looks like a great resource.
-S