I realize this is a bit old, but I ran across it again and realized that I'd never put in a link to it on any MarsWatch links pages—something I'll be fixing soon.
So it seems that Google decided to put is powerful maps interface to work on various Mars data sets. If you go to www.google.com/mars you'll see their standard map interface with the Mars Global Surveyor Mars Orbiter Laser Altimeter (MGS-MOLA) elevation map. You can double-click on any region to center it, zoom in, zoom out, etc. It works just like their regular map interface, although no streets view or traffic reports.
Aside from the elevation view, you can choose the visible or infrared views instead. The visible map is made from a mosaic of images taken with the MGS Mars Orbiter Camera (MOC). The zoom capability here is great! Just check out this view of the Olympus Mons caldera or this area of Candor Chasma. Really nice stuff.
The infrared view comes from the Mars Odyssey Thermal Emission Imaging System (THEMIS). While it is mostly a greyscale image (bright = more IR emission, dark = less IR emission) the brown areas are places where they have added some very high resolution mosaics.
To help you with your exploring, there are links that will highlight various features, spacecraft landing sites, and even NASA stories. About the only thing to be careful about is that when you are hand scrolling around, or you zoom out "too far", you see that the map is repeated several times—so, no, there really are not 4 Hellas Basins on Mars.
Check it out and have fun doing your own "roving" on Mars!
P.S. If you're interested, there's also a Google Moon.