Google Earth now includes Mars. It is free and uses updated photos taken by NASA. Besides being able to explore the red planet and its features, it also includes an interactive tour with Bill Nye the Science Guy, visits to landing sites of craft that have visited Mars, historical maps and a whole slew of other educational material.
If you are interested in the rest of the solar system and deep sky objects (e.g. galaxies and nebulae), they also have a Sky view. This allows you to explore a plethora of objects and plenty of info about these objects. This is definitely a must see for anyone interested in astronomy.
Below is a video tutorial for exploring Mars. Or go straight to Google Earth and start exploring.