Have you ever been to www.themeworld.com?  They have desk top themes that are incredible.  They have so many categories such as:  art, nature, movies, computers, education, sci-fi, products, sports, and games.  They have wallpaper, screensavers, and you can pick a different font whenever you feel like it.  They get new themes all the time and even list the newest ones, daily.   Themeworld offers some 3D themes that have great visual impact.  You will find a huge selection of themes at www.themesunlimited.com/ also.  By the time you investigate these two web sites, you will have enough of a selection to be able to change your screensaver or theme everyday of the week for a year.