Mac OS X (Leopard) only: Virtual desktop enhancement utility SpaceSuit assigns separate wallpaper images for each Spaces virtual desktop so you can distinguish between desktops at a glance.
Once installed, using the application is as simple as switching to a virtual desktop and dragging a wallpaper image onto the SpaceSuit icon in the dock, repeating again for each virtual desktop. The application doesn't replace your current wallpaper, but adds a new layer over top—meaning that SpaceSuit needs to be running and added to your startup items if you want multiple wallpapers. SpaceSuit is a free download for OS X Leopard users only. Hit the link for the download or take a look at the Switching to Mac tutorial for the full walkthrough.
SpaceSuit [via Switching to Mac]
