I love to see bits of mosaics and patterns incorporated into larger LEGO creations. Alex P. (Sirens-Of-Titan) has been making some incredibly neat castle scenes over the past year, and my favorite parts are always the bits of mosaics that he incorporates into the design. These bits can be found on floors, walls, windows, and doors, and add lots of visual interest to the larger creation.
One of my favorite examples is in his Tower of the Arcane, where mosaics are used as pictoglyphs that hold secrets of magic:
Another one of my favorites is the City of Omurtag, which features mosaics running up, down, and all around its walls and floors.
The throne room for that Dwarven City is also covered with mosaicky goodness:
And finally, here is an image that shows mosaics used for a rug as well as for stained-glass windows:
Be sure to check out Alex's photostream for all sorts of fantastic castle MOCs. I also collected some of the best examples of his incorporations of mosaics into a flickr gallery, which you can see here.