Community graphics for sites?

I've been looking around for graphics available to use for a SF related site.  I've not found anything yet.  The project I am thinking about is creating a sites.google.com for an adventure module based on content from my online multiplayer game (in-development hobby) &amp; past short story writing projects.<div><br /></div><div>Is there a zip or directory-listing somewhere of images that are available to use?  Are there images available to use in the first place?</div><div><br /></div><div>Are there banner images to link back to this site (and some of the other popular SF sites)?</div><div><br /></div><div>Thanks for any pointers!</div>