Here's what NASA has to say:

Go to: http://nssdc.gsfc.nasa.gov/planetary/planetaryfaq.html#marsgen-face

There are a blue zillion sites out there, most of which are pro-intelligent design/consiracy theory in nature. Do a dogpile search (www.dogpile.com) using "mars face", "mars pyramids", "mars anomolies", "mars enigmas", or the like. You'll get more hits than a hippy at Woodstock.