Peter from BBextras used to release some hot themes until he had to pull them a bit back. He has always been a photography buff and you can really see what I mean if you check out some of his pictures on www.bbextras.com.
He has some great images that make perfect wallpapers for your BlackBerry but you may need to resize it yourself to fit the background. You also need to register for the site to send them to your BlackBerry which is a bit annoying but the pictures look awesome.
Check them out at www.bbextras.com.