I'm from across the pond but had a go shooting at SEA earlier last month.
When landing from the north I found a spot at Seattle Utilities water tower at the junction of South 146th St. and 24th Avenue S
Its on the hillside so the planes are fairly level on approach. Sun best in mornings.
Had no problem from the golf club car park - do people actually try and photograph from the course???!!
Notables when I was there with ACTUAL times rather than scheduled times
11.34 NW 74F arrives
11.41 Asian 772 arrives
12.03 Vanguard MD80 arrives (daily) - well, it did then!!
12.14 China AL 74F arrives
12.23 Aeroflot 777 arrives
12.53 Allegiant MD80 arrives (not regular?)
08.48 Evergreen DC9F arrives
08.50 Tradewinds A300F arrives
09.04 Hawaiian 767 departs - can be got from golf club
10.01 Hawaiian 767 departs - can be got from golf club
10.12 Frontier 732 arrives (daily, often 733)
10.17 America West 752 arrives
10.48 World MD11 arrives
11.26 ATA 738 arrives (was 10.38 Thurs.)
11.42 Vanguard MD80 arrives
Thursday (seen from Delta departure lounge)
10.20 Omni DC10 arrives
10.36 Sun Country 738 departs
similar time a China Eastern MD11F arrived, later departed
Afternoons - not aware of a good spot for the sun .
I've also tried Renton, BFI and Everett, and you just have to make the best of these places. BFI has a number of cargo movements between 17.30 and 20.00,not only the big jets but 'cargo commuters' too. Try the museum car park for these.
Near the SW corner of Renton there is a small roadside parking lot where you can oversee the field to see whats there. After that try the inner airport perimeter road (dead end) and then go further round on the public road "following your nose" - another dead end! At the NE corner by the lake (access near a railway and some new apartments) you may see a couple of newly finished 737s but these would not be photographable. Indeed, its difficult for pictures here generally, but you may be OK, but always watch out for security at any Boeing airport - have you seen the photos by Royal S King?
At Everett, there is the Museum of Flight store which is usually accessible- the United 727 and Comet are outside with others. The Bo247 is hangared here. Lots of interesting stuff. They make replica Me262's at this field too. Didn't have much time at Everett, but it seems some photos are possible, at Goodrich at least.
I don't know how far your interest extends, but there are other things to see away from airliners. Auburn (not far from SeaTac) has some AN-2's. Arlington has a Dakota. Also,Kenmore Harbor for the Otters and Beavers - Kenmore Air have one or two other bases around here where they fly schedules.