Yes, you can find free photos on the net which you can use on your website. (And no, I'm not talking about Google image search). The problem is, everyone else can find them too, so it's possible your images might look kind of familiar. But if that doesn't worry you, go for it.
DeviantArt Much less conventional than standard photo collections - but more likely to fire your imagination.
FreeImages A reasonable selection, and the images tend to be a decent size.
FreeFoto A large choice, but photos are watermarked and of medium size.
StockXCHNG An impressive range of free photos.