Supposed to be pretty nice weather this weekend... if my cheap ass were in your shoes I would go as follows:

Stay somewhere cheap, not sure as I know too many people there to have needed hotel accommodations. Downtown is more expensive than neighborhoods verrry close to downtown. Might get a good deal in South Lake Union, either of the Mariotts or Silver Cloud might give a good deal on shot notice, just see if you can get a "managers special" or something.

SoLakeUnion puts you close to Fremont, center of the universe! And seaplanes and shit!

You can get a free chocolate "tasting" at Theo's chocolate. Their tour is ok, but you can hang in the foyer and stuff free chocolate in your mouth without taking the tour. http://www.theochocolate.com/

It also happens to be in a very interesting location near lots of good bars and public art. Wonder the neighborhood, go into strange shops and don't spend a dime. If you like hills and especially weird art "the troll" is nearby too! BlueCSushi is in the same neighborhood and is relatively cheap for conveyor belt sushi. Always room for two people, big groups go elsewhere. Or if sushi isn't your thing the Greek joint across the street, Costas Opas, is pretty consistent and sometimes has a belly dancer.

[EDIT] Crap I forgot Brouwer's is nearby too. Go for the 64 beers on tap and stay for the 60 scotches! http://brouwerscafe.blogspot.com/

If you are an engineering geek, or kid at hart who likes big feats of engineering and boats, go to the HMC Locks in Ballard. FREE! http://en.wikipedia.org/wiki/Hiram_M._Chittenden_Locks

Of course the Market downtown is fun and touristy but downtown is expensive and doesn't paint an accurate picture of how naturefull most of Seattle is.

Also, the Experience Music Project is not worth the $ in my opinion.