Dogfish would not be very far out of the way between DC and NYC. They have their original brew pub in Rehoboth Beach and their new brewery about 15 miles north of the brew pub. DFH just received permission from the city to completely rebuild the brew pub so if you want to see the original brew pub (it is nothing to brag about BTW but is the humble beginnings of the DFH company) this would be a good time for you. Their new brewery is quite nice, if you make this detour you should definitely check that out too.
There are several respectable breweries in that area that have not yet quite broken out on the national stage including (in no particular order); Mispillion Brewery, 3rd Wave Brewery, 16 Mile Brewery, Fordham/Dominion Brewing, and Evolution Brewing. If you made the trip to Rehoboth you would pass within a few miles of the first three. The fourth one is in central Delaware so once you turned north for NYC you would pass just a couple miles by it.
Oh, and by the way, don't have too much fun at our Delaware beach areas-we already have too many out of staters bogging everything down. ��
That state on the east side of our river and bay has quite a few breweries too and you could take the ferry across the Delaware Bay to get there if you wanted to make a tour of that whole state. Though that would not be the quickest route from the Rehoboth area to NYC.