UW Green Bay switched its e-mail from arial to century gothic to save ink. They are very similar fonts, but arial has heavier lines. Link
As commenters point out, not printing e-mail saves 100% of the ink. The comment about font width is not exactly correct - century gothic is larger overall, so you should shrink the font size as well. Arial 11 is the size of century gothic 10.
Thanks for the tip, Janet