Our hotel desk staff in San Antonio recommended Corpus Christy Beach for a day trip, we went, spent the big part of a day there and look back on it as being one of the best parts of our vacation. The beach was clean, the water was nice but a bit cool (April) and the people there were very friendly but not intrucive.
Lots of shells found, some even with crabs in them.
ALSO, if you have kids, buy and take a bag of corn chips. When you hold up a corn chip, the sea gulls loose all fear and while flying will take one from your hand. You under a flock of hovering gulls make a fine photo too.