I spent a disturbing amount of time yesterday browsing the Vladstudio website. The website has hundreds of beautiful wallpapers/background (725) and I'm pretty sure I looked at all of them. You can turn the pictures into jigsaw puzzles to play right there on the website. They also have an iphone app which provides 12 puzzles for free and all available puzzles, forever for $1.99.
Here are a few of my favorites: