We went last December, and flew out of Seattle for the exact same reason as you. The difference between YVR and Sea-Tac is amazing. Especially with the dollar the way it is right now. I tried to do a lot of research about hotels around Sea-Tac and finally decided on the Radisson. The location was the best!!! It is literally right across the street to the terminal. And we used MasterPark to park the car for our trip and that was right next door. So I could park the car and just walk over to the hotel.
The problem we had were the beds. It was bad enough that we were so excited for the next day, but we hated the beds. They were too small for us and I know a lot of people like the adjustable beds. I guess those people like camping as well, because the adjustable beds are just air mattresses. You put more air in to make it harder, and take air out to make it softer. You could take out so much air you could feel the wood frame. Well, none of us got a lot of sleep that night and it really made for a long first day.
I would suggest going to TripAdvisor.com and doing a specific search for hotels around Sea-Tac. I have always loved Hampton Inn's, and the one at Sea-Tac is quite close. Sorry, I haven't found a good one yet. If you find one, please write about it.
Spacemouseneer