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Pike's place market really is a must.
Unless you have $100 to blow on a not-so-great dinner on the top of the space needle, it's not really worth the hype to go up... though you may learn a bit about the geography of the city. The restaurant rotates 360 degrees in about 47 minutes - a little less than the time needed to order and eat your overpriced 4oz of steak.
I'd have to second your trip to Uwajimaya(sp?). Actually, spend a whole morning there - grab a nice chinese breakfast for dirt cheap, and shop for some tasty treats at the grocery. Hotels and other such things are actually very cheap there, so if you haven't booked living arrangements, maybe look for a hotel in the district.
If you like Starbucks, maybe when you're at pike's place you can visit the original. But if you just want a good, fresh coffee, you should be able to find it no matter where you go in Seattle (hint: avoid the green, white, and black logo).
EMP (Experience Music Project) is pretty cool if you're into classic rock music. Admission is relatively expensive, but there's enough to do there to burn at least four hours, if you're into that sort of thing.
Check local events in the Seattle Times. There's always something weird going on somewhere around Seattle, or it wouldn't be Seattle.
If you're the artist type, or fit into any sort of sub-culture whatsoever, spend a day wondering around Capitol Hill, preferably on a friday or saturday. If you're the sort for clubbing, Capitol Hill is the place to go. The state Capitol is not actually located on Capitol Hill, though the urban planner sure wanted it to be...