We have stayed at the Sheraton Downtown and the Marriott Bayside.
We really like the Marriott -- within walking distance of Pike's Market Place.
We also went to the Space Needle.
Check this out:
Free bus - http://metro.kingcounty.gov/tops/bus...attle-rfa.html
Aquarium, Pike place market to see them throw the fish, Duck tour would be fun if you haven't been on one before, Pacific Science Center. If it is nice out, instead of taking a ferry, there is a water taxi to West Seattle, Alki Beach which is a lovely beach with incredible views.