In November 2009 my SO heard about the idea of being a "Weekday Veg" I'm not really sure where, but he decided that we should try it out for health, for money savings, for the environment, and for animals. We're actually weekday pescatarians-- we can eat seafood, eggs, dairy on the weekdays and on the weekends we eat whatever we want.
At first I thought it would be difficult, but it's not really that bad. The main thing was that there aren't very many lunch options besides salad and vegetarian burritos around here, so we actually ended up saving even more money by bringing leftovers for lunch almost every day.
Here's a TED video with Graham Hill discussing the idea.
A year passed and aside from a couple of occasions in which work lunches were at steakhouses that make it impossible to resist, it hasn't been too bad. Of course then in December 2010 my SO read about the Four Hour Body and now our diet's getting complicated.