This is a 64 x 96 stud (that's 2 green baseplates by 3 green baseplates) mosaic of my sister-in-law Sarah and her new husband Phillip. I made it as a wedding present, and they loved it when I presented it to them at the reception. This particular mosaic really shows that you can trade resolution for more colors - that is, that if you have more colors then you can get away with a smaller mosaic and still make it look pretty good. (here the mosaic includes, most notably, lots of pink, medium orange, and sand blue, a little sand green and purple, plus the more common Lego colors)
This is the original photo. Notice how I cropped out much of the space between their heads to make it more intimate, and also painted out the background. For a photoshop amateur like me, this took a lot of work.