I'm not sure if you could technically call it a mosaic, it's more like a sculpture in my opinion, but Flickr user, torgugick, creates this really cool face coming out of a wall of somesort. For those of you that know (I don't ;-P ) he says it's Pink Floyd's "The Wall".
The most incredible part about it is that it is made only out of three different elements! It is made out of 2 types of 1x2 plates, and 1 type of a 1x1 plate. Awesome!