Measurements are something you deal with on a daily basis whether you think about it or not. Either way, ACRE's Units of Measurement print will put these units in the forefront of your mind in a rather lovely manner.
The posters are $24 (including shipping), and feature a number of different types of units, from kilograms and hectares to lesser known measurements like astronomical units and picas. Although most of the units shown are metric, as a reference the prints are pretty useful for those of us using the backwards U.S. system. Plus they're really nice looking. The posters are about 40 inches by 26 inches, and while they'd be perfect for a classroom, they make some nice wall art, too. [ACRE via Swiss-Miss]