I've taken guests from out of town to Sky City, the revolving restaurant at the top of the Space Needle, a couple of times recently.
The weekend brunch at $38.50 it isn't cheap, but if you factor in free access to the Observation Deck (normally $13.50 for adults), it suddenly seems like a reasonable deal.
The food is top notch - there are brunchy options like Belgian Waffles and Eggs Benedict, but for the price Prime Rib and Grilled King Salmon seem like more appropriate choices.
Top it off with a good local wine and sit back and admire the Olympics to the west, the Cascades to the East, and watch the sea planes coming and going from Lake Union.
Definitely a great place to take guest from out of town.