Lego recently came out with a series of models of famous buildings that I would not only enjoy building but would actually display somewhere in my home. Having built countless Star Wars Lego ships and Indiana Jones vehicles for my sons it would be a nice change to build something for me and know it wouldn't end up taken apart to join the amorphous pile of bricks in the boy's room.
There are two series with different levels of difficulty; the Landmark series are tall buildings that have fewer pieces than the Architect series which features Frank Lloyd Wright's Fallingwater and the Guggenheim Museum. The Architect series is fairly expensive for Lego ($50-$100) so I'd have to choose the Guggenheim since I wouldn't buy both. Not to say that Fallingwater isn't an amazing home, its just that it's Lego doppelganger isn't as cool as the Guggenheim's.
In the Landmark series I've already built the Empire State Building, it was very easy but also a pretty cool looking model. I want to get the Space Needle next, that just looks cool. I like that the models aren't too literal, they more suggest the look of the building rather than try to create a detailed representation.