Aperio Lux has released uDesktop 1.0 for Mac OS X, an app that lets you access thousands of widescreen wallpapers for the desktop of your Mac. It requires Mac OS X 10.6.6 or higher, costs US$1.99 and is available at the Mac App Store in the Lifestyle category.
All images are grouped by category and resolution. You can browse the images by date acquired or popularity. uDesktop lets you not only download wallpapers for your desktop but also to access all previously downloaded ones from the Downloads section.
uDesktop lets you set the selected image not only on the main and secondary monitors but also on both of them at once. You can also set it up so the image installs automatically at downloading or so that the image changes automatically on a timer.