Also available from WAS to Portland, Oregon until late May/early June, 2011. Friday and Sunday travel more expensive.
DCA-DFW-SEA-PDX (and vice versa) routings earn 3351 EQM each way, 6702 total, for $228.20 r/t. Roughly 3.4 cents per EQM. Plus
there's free beer on the Horizon Air codeshares between SEA and PDX.