I think the current home screen I have of a mountain is from Zedge. I made my own lock screen wallpaper. Not sure which one is the best app though. I just search the internet for a photo I want for my backdrop and go to that website.
Just search for the wallpaper you want, then go to settings and set it as that. I designed my own wallpaper, though, so I didn't do the first part. Wallpaper Engine is also good.
If you're looking for a real good wallpaper or theme just use the theme store. The good ones cost a couple bucks though. Or you could try your luck with good Lock's "theme park".
