From America Public Media, an interactive game that gives a rough indication of how many 'earths' it would take if every person on earth lived and consumed like "you."

Consumer Consequences:What would the world be like if everyone lived like me

My own score was 3.7 earths, and was a bit higher than others who have played with similar demographics. This is definitely a game, and not a refined tool to assess one's 'footprint', but it is still food for thought.