ok so i wanted to answer this one, too. i have two favorite robots.
(1) gir, from "invader zim". why? because he's so random and funny it's ridiculous. it's nigh impossible to squeeze all of that win and awesome into one tiny little robot, but jhonen vasquez did it.
(2) bender, from "futurama". why? because he runs on fucking alcohol!! how cool is that?? he's rude, crude, and unapologetic. i love him.