depends on what you want to do. shop/sightsee or truly get away.
the place i was just at in mexico isn't on a map, there's a small village nearby but the wealth of my time was spent looking at the ocean and sipping mezcal. this, for me, was the first real vaca i've taken in a long time where i turned off my phone, internets, television, etc and really got away. was nice and is my new fav vaca type.
also- for a late summer/fall vaca you should consider the UCLA game in Cali.
also- if you want to leave US and go somewhere affordable with beaches & BABES, hit up Uruguay.