There's not a lot of Beachfront properties on the East coast that are actually true beachfront properties. Because you can travel in the summer, that opens up all of the east coast as possible destinations.
There are good properties in Mrytle Beach, Virgina Beach and Florida that might work well for you. I'll let other members discuss which resorts they know well as all I can tell you about from personal experience is the one we own at, which is Marriott's Ocean Pointe.
Ocean Pointe is in south Florida and works well for us since we like to take a beach vacationin the winter. South Florida is about it for beach vacations in the winter if you want to remain in the U.S. and still swim comfortably in the ocean. Ocean Pointe is a beach front property with access to the beach over the dunes via a walkway. You do not have to cross a street to get to the beach. The beach, while a public beach, does not have easy access to the larger population and is mostly occupied by timeshare resort residents. At least it is at the time of year we go, which is Nov. or Dec.
Ocean Pointe has a total of 5 heated swimming pools, 4 adult and one childrens wading pool. There are also 3 hot tubs, one which is supposed to be reserved as adults only. There are two fitness centers, a convenince store (although small and expensive), a bar and grill, a Pizza Hut express (limited menu), a Starbucks express (limited menu), internet cafe and childrens activity center. The resort has about everything one would need for a weeks stay without leaving the resort if you didn't really want to leave.
There are also several good restaurants within driving distance and a few within walking distance (Max and Eddies, Johnny Longboats, Sailfish Marina, The Buccanier). There are two entertainment districts for night life called Clematis Street and City Place. While they are area's for dining and entertainment they are also family friendly. There is also shopping from the very upscale (Worth Ave) to typical bargain basement shopping within easy driving distance. A short walk across the island (the resort is on a barrier island called Singer Island) there is charter fishing boats.
On the beach you can rent beach chairs/cabana's, catamaran's for sailing, and boogy/skim boards for floating in the ocean. You can also arrange for snorkel/scuba diving or parasailing.
Basically, we find that Marriott's Ocean Pointe has everything we need within easy reach and are very happy with it. Marriott also has a world wide net work of timeshares for internal exchanges including timeshares in Spain if you decide to stay closer to home one year.
I have pictures of the resort located on my webshots page. The link to that page is in my signature below.
While Ocean Pointe works very well for us, I'm sure others will mention resorts that may also work equally well for you or maybe better. One thing you may want to consider is the cost to get to the resort. There are three major airports within close proximity to Ocean Point. Palm Beach International Airport (15 miles), Fort Lauderdale/Hollywood International airport (60 miles) and Miami International airport (98 miles I think). That may make flying into this resort more economical for you.
As for buying resale or from the developer, resale is always cheaper if you take the time to look and shop. However, I don't see a lot of Ocean Pointe units come up for sale at reasonalbe resale prices but, I don't spend a lot of time looking either. I'm certain that they're out there and I just haven't seen them.
For ourselves we bought directly from the developer. We were at the property a couple of months after the terrorist attack on 9/11/01. At that time, Marriott was very unsure what the travel market was going to be like and they were offering strong incentive packages to purchase. We ended up with a 3 bedroom ocean front unit with purchase incentives of a 7 night Alaskan cruise and a bonus week we used to vacation in Scotland. The value of those incentives brought the price of buying from the developer down nicely in our opinion, we got the ocean front unit we wanted and didn't have to spend time on the internet looking for a deal.