I like beach vacations. I'm currently enjoying the last day of a vacation on Manhattan Beach, which is pretty fine. The beach goes forever. There is a biking/running/walking trail the runs about 35 km (according to my Garmin). Great food, not much traffic (once you get there). I have never seen a bigger beach anywhere. And it is pretty well cared for. I feel this is mostly an adult friendly beach.
If you're a beach person, what do you like?
Here are some others that I like:
Myrtle Beach: First vacation I took was there in my mid 20s. The beach is pretty decent and there is lots of it. There is tons to do. Over the years it has become a bit of a tourist trap, and no matter how many roads they build it doesn't seem to be able to keep up with the increasing volume of traffic. A very family friendly place. And definitely a golf friendly place.
Key West: This is kind of like going to a tropical island without having to get on a plane, or go through customs. Very adult and a world of its own. The beach itself isn't as handy as some other places, but it is a good excuse to rent a scooter and terrorize the streets to and from the beach. The place is small enough, you can get from end to end on a beach cruiser if you prefer leg power.
Sydney Australia: I frequented Manly Beach when I was there, in part because that's where the hydrofoil from where I was staying stopped. Sydney is far and away the prettiest place I've visited. The harbour is fantastic, good night life, very civilized and friendly - and restaurants let you cook your own steak. If it wasn't such a long plane ride, I'd go more often.
Nag's Head: There are other fine towns in the outer banks, but this is where I've stayed. Family friendly, but not as many entertainment options as the more touristy beaches. The water is great, especially if you like a surf. In fact, it is probably better to go there planning enjoying the surf rather than lazing about in the ocean - it doesn't lend itself to that.
Tel Aviv: The water in the Mediterranean is amazing. This beach is big an very pretty. There is lots to do on the beach and room for everything. There are a couple of things that might not be to every body's taste: the armed patrols, starting with the security getting off the plane and the bartering in the marketplace. I just considered it part of the culture and went with it.