If you're in Seattle definitly make a trip up to Queen Ann (the parking up there is free, if you can find a spot!). El Diablo coffee has amazing coffee and great food. Good spot for a morning/lunch. Then next door is a really good pastry shop. In fact, there are a lot of neat little food/coffee spots up on Queen Ann.
Avoid the space needle, it's retarded. Just a dumb tourist trap. The EMP under it can be cool, if they got a good exhibit (right now, if not soon, they are having a Star Wars exhibit which sounds awesome).
Glass garden next to the EMP is a must if you're into artsy things.
There is a pinball museum that is cool. Has a few old wood pinballs, all the way up through the ages to nowadays pinball. Small entry fee gets you all the plays you want (it's not a huge place however). Plus they got beer. Pinball and Beer
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Pike Place is another obvious, but prepare for crowds. (The underneath area is a gem, lots of cool little shops and whatnot)
The oddity shop on the pier is cool, so is the Ferris Wheel.
If you want a fun tour/have kids (kids love this), the Ride the Ducks tour is awesome. Amphibious bus that takes you around town, then pulls into the bay and tours a bit of the bay.
Honestly there is a lot to do in Seattle, but those would be in my top if I was visiting for the first time. Watch out for the construction going on downtown.