U.S. Powerboat Show in Annapolis: Oct 14-17, 2010
http://www.usboat.com/us-powerboat-show/home
U.S. Sailboat Show in Annapolis: Oct 7-11, 2010
http://www.usboat.com/us-sailboat-show/home
Note: The Sailboat show is a day longer, and ends on a Monday.
Tha Atlantic City In-Water Powerboat and Brokerage Yatch show is also a big one, and less than a half day drive from Washington, DC area: Sept 9-12, 2010.
http://www.acinwaterboatshow.com/
Atlantic City also a big inddor show at the Convention Center in the winter. Feb 2-6, 2010.
http://www.acboatshow.com/
The Baltimore show is a mid-size show, but used to be bigger in the past. January 27-30, 2011.
http://www.baltimoreboatshow.com/
There is also usually the National Capital Boat Show on the second weekend of March at the Dulles Expo Center in Chantilly, VA. It is a smaller show that caters to smaller fish boats and small cruisers, but I thiunk they had one baot up to about 40'. But, mostly fairly small boats.
I thiunk the Washington Boat Show in Washington, DC was cancelled this past year, but it is typically in February.
The Bay Bridge Boat Show is typically in late April and will be April 28- may 1 this year.
They have brokerage boats there, too.
http://www.usboat.com/bay-bridge-boat-show/home