I read this when I was fourteen or fifteen and wanted to reread it again at fifty years because a movie based on it comes out in 2012 called John Carter of Mars That's kind of confusing as the last book in Edgar Rice Burrough's Mars novels is called John Carter of Mars.

The movie has an interesting cast with Thomas Haden Church playing one of the main villains along with Willem Dafoe, Samantha Morton, Dominic West, Polly Walker, and John Ratzenberger playing other characters. http://en.wikipedia.org/wiki/John_Carter_of_Mars_(film)

You can read the book A Princess of Mars online through Project Gutenberg. http://www.cs.cmu.edu/~rgs/pmars-table.html