I have two pre-school aged children, so I end up watching a lot of kids' TV shows. My favorite one, without a doubt, is My Little Pony: Friendship is Magic. Now it's true that I had lots of ponies when I was young, and loved them and saved them for my own daughter to play with. But beyond that, Friendship is Magic has a lot of intelligence and humor that makes it enjoyable. Apparently this show has spawned quite an internet following, which has started crossing over into the world of LEGO mosaics.
The first that I saw was this Rainbow Dash at BrickCon. I'm not sure if it's a mosaic in the strictest sense of the term, but it's definitely meant to be viewed as a two-dimensional creation.
According to the BrickCon MOC card, this was made by Dani Dougherty and Thomas Michon and "needs to be about 20% cooler".
Then there is this rendition of Derpy Hooves, done by Andrew Somers:
Andrew also used Derpy in a parody entitled, "Call of Derpy: Modern Horsefare", dressing her up as a soldier and re-writing the My Little Pony theme song. You can find that parody here.
I found a few more pony mosaics and mosaic-like creations, although the image sharing has been disabled for those photographs.
Natron77 made mosaics of Fluttershy and Twilight Sparkle which he hung on his cubicle at work.
And finally, JK Animation made Rainbow Dash, Derpy Hooves, and Apple Jack, which you can see here.