Hi "Rock Hall"
On York R., I'd recommend York River Yacht Haven
(
http://www.yryh.net/)
Closest to Williamsburg and Bush Gardens is the marina at Kingsmill (
http://www.kingsmill.com/boating/).
A bit pricey, but VERY nice... worth going for a day or two.
There are a number of other marinas in the area... ie...
Riverwalk Landing on the York R at Yorktown
Salt Ponds in Hampton
Hampton City Docks
Smithfield Station (Pegan River off James R)
Waterside (Norfolk)
and others....
You might want to ck out "Cruising Guide to the Chesapeake Bay" for good info.