We had six of us for I-Day, so rented a house from Annapolis Accomodations. Really cool, approximately 100 feet from waterfront.
PPW, I booked in June via one of the travel sites: expedia, orbitz, one of those. Got one of the nicer hotels, the Westin, for like $75. Walked back and forth to yard every day. (1.5 miles) I had a rental car, but parking is a headache. When I first reunited with plebe, I asked if he wanted to me to bring car back and forth and he said "Geez, Mom, 1.5 miles is nothing!" I guess compared to what they did daily all summer, that was indeed true.
You'll be able to get reservations in the spring.