http://gnome-look.org/content/show.php/Bluecurve+GNOME%2BMATE+Theme?content=148927. This is a nice Bluecurve theme that has been tweaked to work with the MATE desktop for Linux Mint 12. The MATE desktop is the best desktop to use at the moment considering the new desktop environments for Mint and Ubuntu are pretty annoying and resource hungry. There is a direct download for this theme here: http://dl.dropbox.com/u/49862637/Mate-desktop/mate-bluecurve-theme-1.0.tar.gz. There is a screenshot here that shows what this theme looks like.
This Clearbox Metacity theme will go perfectly with the Bluecurve style. Bluecurve is the old Red Hat Linux theme that was used in the older days before Fedora Core came along.
This is another high-rated theme for MATE, called Orta, this is a GTK2 theme that is very high quality and will really enhance your desktop. http://gnome-look.org/content/show.php/Orta?content=134123. Screenshot here.
More top-rated themes may be found here, the Gnome look website has the best quality themes and should be your first stop for customizing your desktop. http://gnome-look.org/index.php?xsortmode=high&page=0&xcontentmode=100. Gnome-look allows users that have created a nice theme or wallpaper to upload it to their account and show it off to the world. Here is a Metacity theme I created in 2007. This is not the best theme but it is worth a try anyway. Get it here: Smokey SVG. Maybe someone will like this theme and use it on their computer. More of my artwork submissions may be found on this page: http://gnome-look.org/usermanager/search.php?username=bejiitas&action=contents.
This is an example; a lovely long exposure photograph that I took, this is a very nice night-time river image that features lovely blurred moving water.
Get high-quality wallpapers here: http://digitalblasphemy.com/freegallery.shtml. The Digital Blasphemy website has a collection of the finest 3D rendered wallpapers, these are the best wallpapers for any desktop. The author of these wallpapers, Ryan Bliss is a master of 3D rendering and anything he creates is a masterpiece of computer artwork.
Using Google Images is another way to find high-quality photographs that make good wallpapers. Google images search. And you may select which resolution you are searching for to match the resolution of your monitor(s).
Finally, the 4walled website is a scraper that hosts incredible wallpapers. A sample search: http://4walled.cc/search.php?tags=space&board=2&width_aspect=&searchstyle=larger&sfw=0&search=search. There is also a report feature that allows the users to weed out desktop screenshots and keep only the top quality desktop wallpapers that are amongst the most stunning images around.
Wallpapers are very important on a desktop; they make it look very good indeed and the ability to change wallpapers and themes is a good feature of the MATE and Gnome Shell desktops. Here are a few nice examples.
http://www.golfwallpapers.net/Images/Majorca-Golf-Course-Wallpaper.jpg Beautiful Golf course photograph with mist.
http://i.imgur.com/T34yU.jpg A photograph of a tree hanging over water with a beautiful green color.
http://i.imgur.com/yAxsH.jpg Photograph of the Rocky Mountains with absolutely stunning colors.
http://blog.logomyway.com/wp-content/uploads/2011/08/hdr-sunset_soon_forgotten.jpg HDR Sunset wallpaper with stunning colors and a road winding through the picture.
http://fun54.com/wp-content/uploads/2012/02/Awesome-most-beautiful-greeny-mountains-sunrise-picture-golden-sun-shining-in-the-sky-nature-view-background-hd-wallpaper-1920-x-1080.jpg Sunset over green fields. Awesome lighting and camera angle.
Last but not least, we have a gorgeous Japanese wallpaper in HD: http://www.highwallpapers.com/wallpapers/beautiful-japan-cg-HD_wallpapers.jpg.