How about using a font that looks at least a little like the original used? That's where, graphically-speaking anyway, the impact of the poster comes from..
I read those links when choosing the font, and several others as well. The font I picked is a Google web font (Cabin) which is closest to Gill Sans, which is pretty close to the original. I should probably use the thicker version, though. Thanks for the feedback!
http://www.k-type.com/?p=2199 or http://www.dafont.com/forum/read/4200/keep-calm-and-carry-on...