Most folks have the right idea; I don't think Dorsett is a 3rd liner on this team, and even though I'm one of Kreider's biggest detractors I'm willing to pencil him in on that 3rd line provided he doesn't become a problem defensively.
I'd go with
Zucc-Richards-Nash
Hagelin-Stepan-Callahan
Kreider-Brassard-Clowe
Asham-Powe-Dorsett
I didn't think we'd see Boyle, I still don't know if we will.My one issue with our roster as constructed is that We have a lot of forwards who are not great defensively. Washington is a prime offensive team,and we don't want to get caught with only 2 men back frequently. Girardi will get worn down facing Ovechkin rush after rush by himself. For this reason,I'd match the Stepan line with the Ovechkin one. It might negate some of their offensive abilitiesby playing simpler and more conservatively, but its the best defensive line we have.