Here's what you all need to know!
The highlights of Aviation in the Seattle Area (from a local's perspective):
#1 KPAE Paine Field the Boeing widebody plant tours & gift shop. 747s, 767s and 777s being built. As of 1/16/04 the tour is only $5.00/person.
Also at KPAE at the other end of the airfield is the Seattle Museum of Flight Workshop where some unofficial tours are available if you call ahead. The have the first 727 a Comet 4 and a bunch of other aircraft that are being restored. Don't hang around too long or they will put you to work cleaning old aircraft parts. . . Lots of opportunities for volunteers to work on museum projects.
#2 KBFI known as "Boeing Field" the museum of flight with the Blackbird, Air Force One (707), Concorde, Stratojet, and too many other great ones to list here. The gift shop here is excellent bring plastic! (This is the best one relative to the one at KPAE.)
Also the Flightline at the north end of the field is the Pre-delivery area for the single aisle planes and near the museum is the "spook" shop with all of the AWACS and ECM test aircraft.
Plus intro helicopter lessons are available here in a Robinson R22 as well.
#3 Kenmore Air on Lake Union and the Main base at the North End of Lake Washington. Go for a Seaplane ride to Victoria BC
just for the day VFR at 3000' is the most fun of all. And Where else can you get airline service with a Radial Piston Aircraft these days?
Kenmore Air and Chrylser Air have introductory Seaplane Lessons too.
Seattle is famous for Jet Airliners but my preference is for the tiny props w/ floats airliners that are ubiquitous to Seattle.
#4 KRNT Renton Plant 737 and 757 Assembly no tours but a slow drive around the perimeter fence is somewhat interesting.
KPAE is about 20 miles North of Seattle KBFI is just south of Downtown Seattle note that KPAE is in the next county and not in Seattle proper so get a map and don't get lost!
My recommendation take the floatplane to Victoria BC
Harbor in the morning go to the Empress hotel for tea (Just across the street from the seaplane dock). And fly back to Lake Union for dinner.