I like to change my personal computer wallpaper once a week, almost always on Mondays, and I usually pick something themed to current events or the season. I know there are hundreds of wallpaper sites out there, and my favorite free wallpaper sites change every few months, so this sampling is just a snapshot of what I currently use.
Digital Blasphemy (free gallery)
Free Desktop Wallpapers
What does this have to do with saving or making money? Maybe nothing, but they are free, and a few could even be inspiring.