pouët.net

From http://www.adafruit.com/blog/2010/04/21/resisty-resistor-captcha-solve-the-resistor-values-to-post-a-comment/
and http://wordpress.org/extend/plugins/resisty/

sweet

awesome, more javascript dependency :/

Gargaj, I agree. I, too, prefer basic functionality to be, well, functional without scripting and/or plugins.
However, this is an -extremely- geeky case, where it is somewhat justified, imho. :-)