In re 2: pop pop hit some good ones. St. Helens and Rainier. Other typical tourist stuff in Seattle is also Space Needle, Pike Place Market and the fish throwers & first Starbucks (always amazing how many people get a pic of that). Chiually (?sp) art glass.
Don't forget the North Cascades if you're thinking of St. Helens or Rainier. A nice loop drive trip is north I-5, east Highway 20 through the North Cascades National Park, S / SE Hwy 153 through the Methow (pronounced MET-how) to the Columbia. From there, a side trip out and back east to the Grand Coulee Dam is a possibility. If not, then south on 97 to Chelan - optional trip up lake here to Stehekin for backpacking / camping. Continue south on Hwy 97 to Wenatchee then head back west on Hwy 2 via Leavenworth or go south Hwy 97 from Hwy 2 to I-90 then back west on I-90.
While doing the drive loop, day hike north on the Pacific Crest Trail from Rainy Pass on Hwy 20 for 5 miles to Cutthroat Pass (and push north a couple more miles for a super cool view of a glacially carved valley and Tower Mtn). When heading back on the drive loop via Hwy 2, bring the overnight backpack gear and hike north (again) on the PCT from Stevens Pass for ~5 miles to Lake Valhalla and stay the night. Ideal time for the Rainy Pass is late September on a clear, cool early fall day when the Larch's have turned color. Valhalla is best in late August / early September when the bugs are toast for the year, yet there's still good weather. Bring the rock rack, rope & shoes with you and climb the Becky Route on Liberty Bell near Washington Pass on Hwy 20. Lots of other hikes / climbs / camping options on the loop.
More options: Hike up Mt. Adams via the south side. Take a kayak trip / tour around Lake Union. Day hike the Issaquah Alps or anywhere on the I-90 corridor (maps from the flagship REI store in downtown Seattle - Granite Mtn, Mailbox, Tiger Mtn, Kendall Katwalk, Lake Annette is a nice overnight trip). Do a walk on ferry ride from Seattle to Bainbridge Island / Winslow - walk off for lunch and touristy stuff, walk back on for return trip. Check out the Future of Flight / Boeing factory tour in Everett. Snoqualmie Falls. The list is endless......