hmm..google images? or you can try flickr. Make sure you check for creative commons before you use it.

Try stock image sources. Like Stockxpert, iStockPhoto, Jupiterimages etc.
Royalty-free images are available from very low prices actually, and such vendors tend to have large selections. Plus you'd be sure to be on the safe side legally (be sure to read the licence agreements).
There are also some free stock sources (of course pix are of varying quality there), such as Stockxchange (sxc.hu).

Oh right..I figured he was artslons was talking about free images. You can also try Getty