http://www.meatlessmonday.com/why-meatless/
much like the British version, meat-free monday, this baltimore based group encourages folks to give up eating animals one day a week.
with some compelling stats, this link has a few good reasons to give up eating meat for at least one day a week, including the meat industry's high usage of fossil fuels and water.  reducing your meat intake by one seventh will reduce your personal contribution to that huge carbon footprint that is the meat industry.