NXT Spider incorporates NXT Motor shape
This realistic looking Spider project will walk forward and backward in response to presses on the NXT buttons. Designing walking things is hard, and this project cheats in two ways. First, it doesn't carry the weight of the NXT (you hold that in your hand as a remote), and also it really only half walks -- it alternately steps on one side while rolling on the bottom side of the gears on the other side... But it looks like it's really walking! For a nice treatment of NXT animals that walk for real (including a non-cheating spider), see The LEGO Mindstorms NXT Zoo by contributor Fay Rhodes.
What motivated this project was using the shape of the NXT motor as part of the visual design of the creature rather than just finding a way to get it in there and/or hiding it. I was struggling to use the NXT motor in another design, and suddenly it started looking like I was trying to strap a huge ant to the underside of a car or something... So I bailed out on that design and made a spider instead.
I'm a gear-headed engineer type who normally thinks in terms of vehicles instead of animals, so to me the shape and design of the NXT motor is not only strange but downright unhelpful at times. If I had my way, the NXT motors would be compact cubes covered with peg holes on all sides (sort of like the Power Functions motors but with rectangular/flat sides and the dead space used for more mounting holes). Nevertheless, I have tried to use the shape to visual advantage in a few other designs, such as a reindeer body, Santa's body, a dog body, and more subtly as a puppy's hips, or gymnast's legs.
I'm sure that some of the more artistically or biologically-oriented designers out there have done some nice things with the shape of the NXT motors. Feel free to respond with a link to designs in which you have made the shape of the NXT motor work for you or seen it in help in somebody else's design.