I know that mine isn't something nobody else has, because I got the idea from somebody else! But I like to do a "real" bathroom, using the house tiles to build a bathtub, then building a toilet from a plant bowl, barrel lid, clock frame, and a lockpick. I also use the elven wash basin, and voila. Bathroom
I'm also a big fan of the gray-and-white checkered floor for kitchens.
One thing I like to do with flowers along the borders of a house or patio: put down plain poppies and then stack snowdrops on top of them and raise the snowdrops 1 or 2 ticks. It makes a cool effect and looks a little more intricate than either of the plants by themselves.
Here are some of the houses I've done (several of which were inspired by designs I saw online):
http://www.flickr.com/photos/phlyers...7594443705051/