Maps-For-Free has produced a nice Google Maps application that lets you view a number of relief map layers.
Not only can you use the application to view the relief maps you can add them to your own Google Maps. Maps-For-Free offers free relief maps and other additional layers which can easily be integrated into your own Google Map projects.
A drop-down menu at the top of the map lets the user select from a number of relief map layers, including forest areas, swampland, tundra and many more. The application also includes a nice snapshot tool that allows you to define an area of the map and grab a still image.