Thanks for all the replies - I'm surprised I did not figure out how to do this myself... ;-) I found a $360 fare which is not so bad...
My motivation for flying into IAD and our of DCA is simply to make life easier for my GF whom lives in D.C. (and I live in SEA...). I'm meeting with her in IAD (we are arriving on different flights) and she lives much closer to DCA...plus I'm meeting up with a friend for the ORD->SEA portion (complicated - I know ;-))