Over in South Lake Union, Courtyard by Marriott-Lake Union (925 Westlake Ave. N, 206/213-0100 or 800/321-2211, www.courtyard.com [1], $159–189 s or d) is a good bet, convenient to the lake, the freeway, and Seattle Center [2]. Rooms are what you would expect from this chain, complemented by amenities including an outdoor pool, hot tub, and exercise room.
Links:
[1] http://www.courtyard.com
[2] http://www.moon.com/destinations/washington/seattle/sights/seattle-center-and-belltown